Let's say that science proves that God exists

[Esquilax]

I agree atheism doesn't mandate atheists subscribe to any particular belief or philosophy. Nevertheless, if true human beings are nothing more than the unintended consequences of the laws of physics and from that point of view there is nothing special about humans, they have no special rights, they're not endowed with unalienable rights. You can't infer from that perspective that humans have a right to live. What right does something that was never intended to exist in the first place have to live? On the other hand if the universe was created for the purpose of hosting human beings then we do have a philosophical basis to infer that humans are special, should have special sanctions such as the right to life and equality. Doesn't mean we do those things perfectly, but we do have a basis for it.

Wow, um, seriously? You gonna put that strawman out in a field to scare some crows, or just keep it to yourself?

As a human, I have this thing called empathy, which allows me to interface with the experiences of my fellow human beings. In having this ability- and since we're herd creatures evolution no doubt sharpened this sense in most of us- I am willing to allow other humans certain rights that I would like to have myself. These rights come from social agreement; to imply that they come from god or some inalienable extra specialness we all have is patently ridiculous because those rights haven't been a stable thing throughout all of human history. If they were external they'd be stable, but they aren't; plenty of societies throughout history have had differing versions of those rights, or no rights at all, or differing rights that we don't have now. Autocracies still exist, after all, where the rights of the people are predicated on the whims of the ruling class.

Besides, we don't need a philosophical reason to have these rights; practicality will do just fine, for the survival of our species. That's what empathy is for, really: it's a mental response to effects that may be harmful to us.

And hey, that's even ignoring the fact that the bible sets out clear rules for slavery, if you want to talk about inalienable religious rights...