Atheism is the absence of a belief in the supernatural, nothing more. Your personal philosophy inclines you in the direction you have described, someone else who happens to be an athiest may have a similar point of view or one diametrically opposed.

"Christianity . . . tells believers that it's ok to conquer and slaughter the non-human animals" (?)

Good grief, Steve.

So we would all be peaceful vegetarians (living on the Crass commune?) if wicked, old Christianity hadn't told us to go eat cheeseburgers.

Actually, the only philosophy - religious or otherwise - that specifically forbids eathing animals is (I believe) Buddhism . . . which is - Presto! - a religion.

Good Night.