Vic Mackey shot another cop in the head just to keep his criminal enterprises going. Shane Vendrell is a racist half-wit who is trying to follow in his footsteps. I have no idea what's wrong with Ronnie and Lem, other than the fact that they're followers who just do what they're told most of the time.
These are bad guys. They are entertaining and interesting bad guys, but they're bad guys all the same. That's what's brilliant about the show; from the very first episode, the foremost main character did something that would forever make it impossible for him to be anything but a bad guy, and the viewers who still want to watch love him anyway. I see no problem in that premise, but I have a huge problem with the degenerate scum among the viewers who actually act as if Vic and Shane (perhaps not Lem and Ronny... yet) shouldn't be dead or in prison. Vic is a sociopath. He's got his twisted code of ethics and he's done plenty of things that are "good" in the end, but he's a sociopathic criminal nonetheless. Is he charming and charismatic? Absolutely. Most successful sociopaths in the real world are. That doesn't make what he does okay.
I don't have any love for the criminal justice system. I think it's a sick joke and a faulty crutch for society that needs to be rebuilt from the ground up. My assertion that Vic is an irredeemable villain is not based on a strict interpretation of the law. Since this is a comic book superhero site, I'll put it in terms most of us can easily understand: Vic is like Venom, but worse. Venom fights evil to make himself feel good about himself (like all true do-gooders do, as well as self-righteous hypocrites) but instantly turns into a vicious murderer if someone gets in the way of his committing acts that benefit only himself (like killing Spider-Man). Vic killed a cop who threatened his criminal career, just like Venom killed several cops in his quest to kill Spider-Man. Venom is a selfish maniac who can never accept the blame for his failures and has even killed innocent people in his vendetta against the enemy he irrationally hates, but he doesn't deliberately keep drug dealers and violent criminals in business. Vic cares about only himself, people he sees as an extension of himself (his kids and his team), people he sees as property (his wife and kids) and people he can exploit (Lem, Ronnie and countless others) as far as they're useful to him.
I know society is hopeless as far as priorities go, but I reallly hate to be reminded. That's what it is when people start believing idiotic notions like sociopathic dirty cops being the good guys.