Kaffee: It was oregano, Dave. It was 10 dollars worth of oregano. Lieutenant Dave Spradling: Yeah, but your client thought it was marijuana. Kaffee: My client's a moron that's not against the law. Lieutenant Dave Spradling: Kaffee, I have people to answer to just like you do. I'm going to charge him. Kaffee: With what? Possession of a condiment?
Your interpretation of mens rea is just way off. If I'm driving a propeller boat, and I kill a scuba diver that forgot to post the bouy signalling his presence, then I haven't commited a crime, because I was unaware, and could not reasonably be aware, that there was a scuba diver under my boat.
On the other hand, if there is a bouy, and I drive over the top without killing the diver, and it can be demonstrated that I was intending to harm the diver then yes, I can be convicted for attempted murder. Attempted murder mind you, and not murder itself. This requires that attempted murder be a crime. Back to our erstwhile smugglers, if there is a crime of attempted smuggling then yes, they should go down for it, as they were indeed attempting to smuggle. If the only crime on the books is actual smuggling, then they should waltz out of the courtroom.