To not believe in afterlife, you explicitly have to not believe it, so even the denying of afterlife is based on a (negative) faith.
Atheists don't seem aware of being their position a simple negative faith response to a positive faith.
But "weak" atheism is merely a rejection of theism. It is not a proposed hypothesis, but a rebuke of unsupported hypotheses.
All things that happen must have a cause.
Even Big Bang had its Cause. And since the exact definition of God is: "The only one not caused by anything, but simply 'cause' of Itself", there's no escape here...