There's an article in the New York Times about officers who question the drug war... and get fired for it. LEAP, an organization I've been part of almost for almost nine years, is well featured.
Hard to imagine a cop being fired for questioning the rationality of any other law. But the war on drugs has always been a bit of an odd crusade that tolerates no dissent. Did officers during Prohibition get fired for saying it didn't work?
Police are asked all the time to enforce laws they don't agree with. I did. I see no problem with wanting to end the war on drugs and being a good police officer. I arrested drug dealing while wanted to see drug legalized... in which case public drug dealers would still be arrested (there would just be a lot fewer of them).