I've Seen - Protestant Evang. Donations Thou shalt not suffer the laborer in Zion to perish. They are a tactic of tyranny. Sure they are effective for catching criminals, but they invade the privacy of the innocent in the process. Effectiveness is not a criterion for whether or not something is right.
Bullies can be very effective in extracting what they desire from their victim.
The fourth amendment of the Constitution calls for the right to privacy and security against unreasonable searches and seizures. Traffic checkpoints are a direct and blatant violation of that provision. In principle there is no difference. You never know if the enforcement official is a gestapo type or a friend. The officer might think you have something to hide if you protest.