Atheism is, of course, a belief. It’s a belief that there are not any gods.
The belief that there are no objective moral rules only guides your actions to the extent that it may relieve you of constraints that you might have had if you thought there were any. But whether any other moral code is “better” than this would simply come down to a matter of value judgment.
Who the problem with truthpreservation? It’s a technical term, and i gave a link
Your notion of using metaethical nihilism to guide action is analogous to treating atheism as a belief. Your actions would be unguided.
Atheism is, of course, a belief. It’s a belief that there are not any gods.
The belief that there are no objective moral rules only guides your actions to the extent that it may relieve you of constraints that you might have had if you thought there were any. But whether any other moral code is “better” than this would simply come down to a matter of value judgment.