Anyway, this is another underhanded discussion tactic. Someone should really come up with a name for this informal fallacy. Maybe we can call it "argument by 'oh yeah, and what have you done lately!?'".
I think it is the "Only cops are qualified to judge a cop's actions" fallacy.
I see it commonly used to rebuke criticisms of cop shootings. WE weren't there. WE don't know what cops have to deal with. WE can't understand.