Willfulness is a completely different thing that knowing the law. Willfulness only requires that I intend to do what I did, not that I knew it was illegal.

If I somehow don't know that killing people is illegal and I intentionally shoot someone, the excuse that I didn't know it was illegal doesn't get me anywhere (even assuming the court believes me).

If, on the other hand, I didn't intend to kill someone, that does lessen the severity of the crime or even eliminate it if it was truly a freak accident where I couldn't reasonably have prevented it by exercising more caution.