Not knowing that what you are doing is illegal is not a defense for you, true. But when a cop arrests you for doing something they believe is illegal but in fac

Not knowing that what you are doing is illegal is not a defense for you, true. But when a cop arrests you for doing something they believe is illegal but in fact is legal, you are not allowed to resists arrest. You must allow yourself to get arrested (and searched) and then explain later, at the precinct. You'll lose a few hours, people will be worried about you, you might lose your job, and the police don't owe you anything, because cops do not have to know the law. Only prosecutors are supposed to know the law, and then only if a judge is willing to shame the prosecutor (not a given).