Only bad ones at bad places. I used to be a bouncer for years.
I was a guardian of "you" and my bartenders. I got you home safe, got rid of sexual predators and creeps, and gave you a light for your cigarettes and joints even though I don't smoke either anymore. Someone to chat with at length when you were just there because you had to. I suppose I would boost the occasional self-esteem too :]
I would also beat people up and sometimes pepper spray their mouth and eyeballs if they were violent assclowns. Such is life!
I was only being half serious. I was mostly referring to "trendy places" that profile patrons, often racist etc. I do know many good bouncers at good establishments and they try to filter out dangerous people, like drunk/high dudes or bachelor/ette parties.