While I don't disagree with the sentiment, since you have a friend who's a cop I'm compelled to ask the uncomfortable question, is an otherwise good cop who protects bad cops still a good cop?

That’s a good question.

You know how all the people taking part in a robbery get charged with murder if just one of them kills someone?

I’d view it like that. A cop that covers up corruption for a partner is guilty of corruption. A cop that covers up a DUI carries a similar amount of guilt.

A cop that exercises ‘professional courtesy’ to overlook a minor traffic violation? Same negligible amount of guilt.

I think it seems about right.