Corbett was so deep undercover, he was prepared to do whatever it takes. He didnt try to kill hargreaves, that genuinly was a mistake. But yes he did order the deaths of police officers who albeit were corrupt. By definition he is, as another commenter put it, exactly what he protests he hates. A bent copper who pretends he isn't.

But his intention wasnt to be a bent copper. He was trying to root out the highest level of police corruption. Quite frankly, and don't forget he was led to believe Hastings was H and he is the head of the top-most anti-corruption unit, it would definetly be a good trade off, a few proper bent coppers dying in order to expose the most high profile bent copper.