> “Mens rea” is a key component of most crimes. Some crimes can only be committed if the perpetrator knows they are doing something wrong. For example, fraud or libel.

We're talking about orthogonal issues.

Mens rea applies to whether the person performs the act on purpose. Not whether they were aware that the act was illegal.

Let's use fraud as an example since you brought it up.

If I bought an item from someone and used counterfeit money on purpose, that would be fraud. Even if I truly believed that doing so was legal. But it wouldn't be fraud if I didn't know that the money was counterfeit.