> But this is how it always goes with religions. There is never a definitive core belief or core morality that everyone agrees with.
The vast majority of Christians would say that belief in the existence of God is a core belief of Christianity. They'd say an atheist is by definition not a believer in Christianity. And, up until the 20th century, there was universal agreement on this. Then, along came some people who claimed they could be "Christian atheists". However, even today, those people are a tiny minority of (self-described) Christians, the vast majority of Christians don't accept that as a valid form of Christianity. In fact, even most non-Christians, even most atheists, don't accept that as a valid form of Christianity. I expect you'll find Christian atheists to be greatly outnumbered by those atheists who consider "Christian atheism" to be a silly oxymoron.
Similarly, in Buddhism, up until the 20th century, pretty much everyone agreed that rebirth was a literal phenomenon – not just some kind of metaphor – and that was seen as a core belief of Buddhism – they would say that a person who does not believe in literal rebirth, by definition does not believe in Buddhism. Nowadays, there are a lot of people – especially in the West – who disagree with that, and think that "there is no afterlife, rebirth is just a metaphor" is a perfectly legitimate variety of Buddhist belief – however, I'd be surprised if people who define "Buddhism" so broadly are any more than a small minority of all Buddhists globally.
The vast majority of Christians would say that belief in the existence of God is a core belief of Christianity. They'd say an atheist is by definition not a believer in Christianity. And, up until the 20th century, there was universal agreement on this. Then, along came some people who claimed they could be "Christian atheists". However, even today, those people are a tiny minority of (self-described) Christians, the vast majority of Christians don't accept that as a valid form of Christianity. In fact, even most non-Christians, even most atheists, don't accept that as a valid form of Christianity. I expect you'll find Christian atheists to be greatly outnumbered by those atheists who consider "Christian atheism" to be a silly oxymoron.
Similarly, in Buddhism, up until the 20th century, pretty much everyone agreed that rebirth was a literal phenomenon – not just some kind of metaphor – and that was seen as a core belief of Buddhism – they would say that a person who does not believe in literal rebirth, by definition does not believe in Buddhism. Nowadays, there are a lot of people – especially in the West – who disagree with that, and think that "there is no afterlife, rebirth is just a metaphor" is a perfectly legitimate variety of Buddhist belief – however, I'd be surprised if people who define "Buddhism" so broadly are any more than a small minority of all Buddhists globally.