I don't know whether that's true or not (it's certainly a libertarian talking point I'm familiar with), but most criminal statutes are not strict liability.

This argument is besides the point, though. I'm not saying that contempt rules are OK because the underlying crimes require the state to prove mens rea. I'm saying, the court has for centuries been charged with ascertaining truths that are in some sense unknowable, because they depend on determining what someone was thinking. This isn't a new challenge for the court.