Well, no. Atheism does not purport anything to be true at all.
It's a lack of belief in one thing. I don't understand why that's so difficult for religious people to understand. Atheism is not a replacement for religion. There is no atheist rulebook, no set of beliefs, nothing.
Atheists can of course have morals but they don't derive from atheism and are not hindered by it either. They're unrelated.
*Edit, expanding...
Your argument presupposes that the only place morals can be derived from is religion where that the rules exist is the entire argument for why you should follow them. God says so, end of discussion.
There are better ways to derive morals based on day to day reality. There are better reasons not to murder than god says so.