I can't figure out his status.
The commissioner admits that McLain came to him with Serpico's allegations. So that would suggest that McLain might be good?
But McLain also flips out when Serpico says he went to outside agencies. He also tells Serpico that the Bronx division is clean when, in truth, there was heavy corruption there.
Was McLain corrupt or honest?
He was the one who tried to get Serpico to go to the Catholic police officer's retreat, right?
I think he wasn't specifically supportive of corruption but he was a loyal organization man who held up the institution. Going outside the family was worse than taking payoffs, even if he didn't approve of the payoffs.
He might have even had a kind of warped version of what "payoff" meant. Strong-arming lowlifes into payoffs might have been seen as good policing -- more or less containing vice, even if it involved putting illicit money in your packet. Actual corruption to him might have been doing bidding for criminals, like carrying out tasks for a mob figure or something.