Let's be fair about this. You have a right to mouth off to a police officer as much as the police officer (in this case) had a right to arrest the offender. Neither are necessarily constructive, but simply allow stubborn people to prove some point. Practically speaking, one has to ask if proving that point (whether it's a point about morality or about power) is worth the risk of negative consequences.

There's a time to exercise your right to free expression, and a time to shut up and let a cop do her job. If you're being wrongly or unjustly persecuted, speak up. When you're pulled over after committing a traffic violation, you ought to shut up.

It bears repeating: treat people with the respect you expect to receive. Cops are no exception.