I would like to place this sentence in context, this is going to be long...
One may conclude from tpk67's other writings that she is declaring that those who chant Nam(u) myoho renge kyo should not dispute with others.
Since tpk66 neglects to place this passage in context with the preceding passage, the three following passages, and the entire canon of Nichiren, one might agree with this shallow understanding. First, here are the preceding and following passages with the passage that tpk67 chose:
"The non-Buddhist schools of such men as Vatsa and Vaipulya, which appeared in India after the Buddha’s passing, are even more wrong in their views and more cunning in their doctrines than their counterparts before the Buddha [because they borrowed ideas from Buddhism]. Similarly, since the introduction of Buddhism to China in the Later Han dynasty, non-Buddhist views and writings have become even more wrong and cunning than the pre-Buddhist writings of Confucianism that deal with the Three Sovereigns and Five Emperors of antiquity. Also the teachers of the Flower Garland, Dharma Characteristics, True Word, and other schools, jealous of the correct doctrines of the T’ien-t’ai school, brazenly interpret the words of the true sutra in such a way that they will accord with the provisional teachings.
Those who seek the way, however, should reject such one-sided views, transcending disputes between one’s own school and others, and should not treat others with contempt.
In the Lotus Sutra the Buddha says, “Among the sutras I have preached, now preach, and will preach [this Lotus Sutra is the most difficult to believe and the most difficult to understand].”
"Miao-lo remarks: “Though other sutras may call themselves the king among sutras, there is none that announces itself as foremost among all the sutras preached in the past, now being preached, or to be preached in the future.” He also says: “Concerning [the Buddha’s statement] that this wonderful sutra surpasses all those of past, present, and future, there are those who persist in going astray. Thus they commit the grave fault of slandering the sutra and for many long kalpas are subjected to sufferings.”
Startled by these passages in the sutra and its commentaries, I examined the entire body of sutras and the expositions and commentaries of the various teachers, and found that my doubts and suspicions melted away. But now those foolish True Word priests rely upon their mudras and mantras and believe that the True Word school is superior to the Lotus Sutra, simply because the Great Teacher Jikaku and their other teachers have assured them that the True Word is superior. Their views are not worthy of discussion."
Here is a better translation of these passages by Kyotsu Hori (with the passage in question italicized:
"Now, as for the assessments of the sutras by the founding fathers of the four Buddhist schools, heir judgments seem to conform, more or less, to sutras and their commentaries. However, they all seem to stick to the teaching of their own schools without correcting the errors of their own teachers. Their opinions are formed from egotism and distorted interpretations of sutras. It is self decorated egocentricity! Men of Vatsiputra and Vaipula Schools, after the death of the Buddha, were stronger in theology than Brahamanism before the rise of Buddhism in India. Confucianism since the Later han, when Buddhism was introduced to China, became more intricate than Confucianism in the time of the Three Emperors and Five Rulers, when Buddhism was unknown in China. In the same way, teachers of such schools as Kegon, Hosso, and Shingon, envious of T'ien-t'ai's true teaching, tend to resort to distorted interpretations of the true Lotus Sutra in order to fit it into their provisional teachings. Surely, those who aspire to enlightenment should not be biased, stay away from sectarian quarrels and not despise other people.
It is said in the Lotus that among the sutras which had already been preached, are now being preached, and will be preached, the Lotus Sutra is supreme. Commenting on this, Grand Master Miao-le states,: 'Besides the Lotus Sutra, some sutras claim to be the king of sutras, but they are not really the first among sutras as they do not claim to be one among those which have already been preached, are being preached, and will be preached.' He also asserts, 'Although the Lotus Sutra is incomparable dharma above all the scriptures preached in the past, present, and future, many are confused about this, and they will suffer for ever from slandering the true dharma."
One might conclude that Nichiren was a hypocrite. He just harshly remonstrated with the four Buddhist schools, labeling their teachers with "self-decorated egocentricity", and concluding, "surely, those who aspire to enlightenment should not be biased, stay away from sectarian quarrels and not despise other people."
In the entire canon of Nichiren, Nichiren wrote more than three thousand references to the errors of the various schools of Buddhism, their adherents, and the non-Buddhists. Furthermore, he wrote dozens of criticisms towards his own disciples who chanted Namu Myoho renge kyo but who embraced the Lotus Sutra (incorrectly). Regarding "surely, those who aspire to enlightenment should not be biased": Yes, not biased towards the opinions of those founding the four Buddhist schools and only relying on the Sutras themselves (particularly the Lotus Sutra). Regarding, "stay away from sectarian quarrels and not despise other people.": One need remember to whom this treatise was entrusted, the Samurai Shijo Kingo. The layman Shijo Kingo was not yet sufficiently knowledgeable to engage in sectarian quarrels. Lastly, regarding "not despising other people", no True Buddhist despises other people. Nichiren, for example stated,"My only hatred is for the act of slandering the Law." He went so far as to call the Japanese "Attorney General", Hei no Seamon who tried to kill him, "my best friend in the world."(because it is thanks to one's enemies that one can attain Buddhahood).
Nichiren taught his disciples not to believe even those who claim to be his followers unless they have some proof of it in his own hand. The proof today is the Lotus Sutra and his authentic writings, believing and upholding them.
Today, it is the various Nichiren sects and their followers who fail to uphold the Lotus Sutra and the writings of Nichiren, yet who call themselves "Nichiren Buddhists" who are to be corrected . Sects such as the Soka Gakkai and the Nichiren Shu who practice interfaith rather than the exclusive faith and practice of the Lotus Sutra are examples of those who fail to uphold the Lotus Sutra and the teachings of Nichiren.
Nichiren admonishes his errant disciples, even those who chant Namu Myoho renge kyo:
“Many such examples of slander are also found among Nichiren’s disciples and lay believers.”
“They entirely look up to groups of icchantikas and rely on them as leaders and, reverencing slanderers against the Dharma, make them national teachers. Taking up the Classic Filial Piety of Confucius, they beat their parents’ heads and, while chanting the Lotus Sutra of Lord Shakya with their mouths, they go against the Master of teachings.”
"You also mentioned in your letter that the people connected with Ōta Jōmyō are apparently saying that the theoretical teaching of the Lotus Sutra can in no way lead to enlightenment. They are making a serious mistake. Remember this about the theoretical and essential teachings of the Lotus Sutra: Which is shallow and which profound, which superior and which inferior, which lenient and which severe, and which subordinate and which primary must be judged in accordance with the time and the people’s capacity. There are three periods in which the sacred teachings of the Buddha’s lifetime should be propagated; the people’s capacity should be thought of in the same way."
and further down
"This doctrine concerning the theoretical and essential teachings is not my own [but was expounded by the Buddha]. Those who would distort it can only be possessed by the heavenly devil, or Pāpīyas, and will topple others along with themselves into the great citadel of the hell of incessant suffering. How foolish they are! Teach this doctrine to others clearly as I have taught you these many years. Those who call themselves my disciples and practice the Lotus Sutra should all practice as I do."
"...Some of my disciples may be asking. “Does Nichiren really have an understanding superior to that of Jikaku and Chishō?”
"The noblest people in the present age are in no way superior to Shakra or the boy Snow Mountains, yet because of my low social position, they have rejected my wise words. That is why the country is now on the brink of ruin. How lamentable! And what I find even sadder is that I will be unable to save those disciples of mine who have pitied my sufferings."
"...Although my disciples had already heard this, when both great and small persecutions confronted us, some were so astounded and terrified that they even forsook their faith. Did I not warn you in advance?"
"...Faced with such criticisms, my disciples became quite downcast and complained that I had been too provocative in my attacks on the True Word school."
"To such a place, where friends from former times never come to visit, where I have been abandoned even by my own disciples..."
"It would seem that Nichiren’s disciples, after journeying to the capital, at first were careful not to forget their purpose, but later, led astray by the heavenly devil, they lost their senses completely. That is the way Sammi-bo was acting. You had better beware that you do not act the same way and incur the anger of heaven."
"Now I, Nichiren, understand these things because of what I myself have undergone. But even if there are those among my disciples who understand them, they fear the accusations of the times; believing that their lives, which are as frail as dew, are in fact to be relied upon, they backslide, keep their beliefs hidden in their hearts, or behave in other such ways."
"Therefore, no matter how I explain and try to persuade my own disciples, they still cannot seem to overcome their doubts, but behave like icchantikas, or persons of incorrigible disbelief. Therefore, I have quoted these passages of explanation from T’ien-t’ai, Miao-lo, and others in order to silence their ungrounded criticisms."
"You should read again and again the previous letter in which I explained that one should of course obey one’s teacher, sovereign, and parents, but should they commit wrongs, admonishing them is in fact being loyal to them."
"It has been twenty or more years now since I found myself in that situation and began the great battle. Not once have I thought of retreat. Among my disciples and followers, however, those who are cowards have for the most part either given in or retreated at heart."
"If you are of the same mind as Nichiren, you must be a Bodhisattva of the Earth. And if you are a Bodhisattva of the Earth, there is not the slightest doubt that you have been a disciple of Shakyamuni Buddha from the remote past."
Grand Master Miao-le was a man of the T'ien-pao Period toward the end of T'ang China. Having widely read and deeply contemplated canons of the San-lun (Sanron), Hua-yen (Kegon), Fa-hsiang (Hosso), and Chen-yen (Shingon) Schools, he concluded that those who do not know of the Original Buddha revealed in 'The Life Span of the Buddha' chapter are like 'beasts and birds, who may be talented but do not know of the land governed by the father. 'No matter how capable he may be' refers to men like Fa-ts'ang and Ch'eng-kuan of the Hua-yen (Kegon) School and Venerable Subhakarasimha (Shan-wu-wei) of the Chen-yen (Shingon) School, who were men of talent but, like children who do not know their father, did not know of the true and eternal Sakyamuni Buddha.
Today, sadly, these last are the men of the Soka Gakkai and Nichiren Shoshu.