I've always heard the phrase "ignorance of the law excuses no one". Now, should it? In many cases maybe so, but we all know the obvious cases where it probably shouldn't.
But to assume that intent is the rule of thumb or has been since... Well, I'm 32 and have never understood it to be. To assume that it is, is odd to me. That's genuinely an attitude I've never heard argued by someone who wasn't an accused party.