Ignorance v. Mistake of Fact

A mistake of law is when you do something illegal but you were ignorant of the fact that it was illegal. That doesn't necessarily mean you're stupid, it just means you don't know all the laws. Let's say you get busted selling crack to teenagers on a high school campus. Can you plead a defense? Well sure, you can be like, "but I didn't know it was illegal to sell crack to kids while they're at school." Even if you actually thought that, not only would you sound retarded, you'd still go to jail. That's because you made a mistake of law, and ignorance of the law is no excuse. But why?

There is some sense to this seemingly draconian policy. People lie. They do it all the time. How can a judge ever really know what you believed? They really can't unless you confess, which let's be honest, who's that stupid? You'd be surprised. The point is that proving a subjective fact is virtually impossible.

Okay, but what if you make a mistake of fact? What then? Mistake of fact is when you know something is illegal but nevertheless break the law albeit mistakenly. Like when a person is shopping and mistakenly forgets to pay for an item. You honestly didn't mean to steal, but did. Most likely you can raise your mistake of fact as your defense and escape liability, if it's a reasonable mistake.

If it's not, well, you're probably screwed.