Does that make it a sin? Commandments are not detailed guides, but general principles. There are clearly accepted exceptions to most of them, including honest belief.

Who exactly is the source you cite for the claim atheism is breaking the commandment and therefore sinful? He does not seem to be a Catholic, let alone someone with authority to define the church's teachings. Can you link to a similar statement in the Catechism, a church Council, or at least a papal encyclical?

"One protestant preacher said" is not proof of what the Catholic Church believes.

> Commandments are not detailed guides, but general principles

That's a far stretch. How is "keep the sabbath holy" a "general principle" in any way? How is "thou shalt have no other gods before me"?

What about "You shall not kill". There are quite a tradition of exceptions. In self-defence (generally accepted), in war (widely accepted, although not by everyone, and always with limitations such as requiring the war is just), and for judicial punishment (although again only as a necessity, and the Catholic Church has said its not necessary under modern circumstances).

The bible doesn't say that. It says "you shouldn't murder" where "murder" means "kill a human without just cause". The standard "thou shalt not kill" is a bad translation, nothing more.

You can tell that it is from context as the laws just after that mandates a LOT of killing. For being "a witch" for example (which I assume is another mistranslation).

Violence can be correct in self-defence and war, but being in self-defense is not enough to justify it alone.

> Does that make it a sin?

Yes the ten commandments are very much what defines sins.

> "One protestant preacher said" is not proof of what the Catholic Church believes.

Yes. From the Catholic Catechism: https://www.vatican.va/content/catechism/en/part_three/secti...

> 2125 Since it rejects or denies the existence of God, atheism is a sin against the virtue of religion.