his physicalism does not preclude nirvana. He can experience nirvana whether he believes in rebirth or not, providing he relinquishes his afflictions. His position is that belief in rebirth is irrelevant to the cessation of suffering.
Is not "liberation" freedom from cyclic existence (a.k.a. samsara), the cycle of rebirth? That's pretty fundamental if one buys the original 4 Noble Truths position that dukha pervades all of life.
You do not have to accept rebirth literally to accept "sarva dukkham". If the solution to suffering in this life is calming the mind with shamatha and developing the insight which burns away afflictions (it is), then what does believing in rebirth have to do with it?
If you have ended your afflictions you won't take rebirth again, according to Buddha's teachings, anyway. So what does it matter? All that matters is that one sees through the matrix of conditions that create your suffering here and now.
This is the minimum requirement.
So, in this thread, we have seen three things:
1) The four seals do not require belief in rebirth
2) Refuge in the Three Jewels do not require belief in rebirth
3) Belief in an eternal unconditioned ultimate is not a requirement to be a Buddhist.
In realty, no beliefs of any kind are required to enter the Buddha's path.
What we need to understand about Batchelor, for example, and many Westerners like him, is that they are trying. They are inspired by the Buddha's example, and they accept what makes sense to them.
Buddhadharma is not about belief and faith. Ultimately, like all Indian yogic paths, it is about personal experience: direct perception and inferences derived from those based on one's practice. It is a personal journey, not one that exists in a catechism. There is no "bible" in Buddhadharma. Rather, Buddhadharma holds a range teachings from belief in an inexpressible self which is neither the same nor different than aggregates [pudgalavadins] to the crypto Vedantic musings of Dolbupa, to the explicit refutation of the unconditioned by Nāgārjuna and the assertion that nirvana is a non-existent [sautrantikas].
So now, Buddhists, you have to make room for a new understanding of Dharma, one that does not include rebirth as a vital central principle. It won't kill you to be generous.