The proportion of bad cops to good cops is probably about the same as the proportion of pervert sexist programmers who like to sexually harass their female coworkers to non-perverted programmers. If your only exposure to either profession is what you see online, you'll have a dim view of both professions.

It's true that there is a large number of bad cops--but that's simply because there are a lot cops. Most cops hold themselves to a higher standard, but never show up in the news because it's not newsworthy when a cop does his job.