Question: If Voight's a dirty cop and everyone knows it why tolerate it? Why not set up a sting and take him down?
Answer: Also, if you watch Season 1 of Chicago Fire it gives a little history of Voight before he goes to jail when he was actually a "dirty cop" and Antonio Dawson is actually the one who takes him down. I found it interesting and was surprised by his character back then.
Answer: And cuz he's only dirty to the bad guys. He takes care of the victims.
Answer: Because he is a great cop and gets the job done better than anyone.