Short answer: rarely trust them.
Long answer: have met plenty of 'good eggs' who join with the right intentions. It takes them little or no time to get institutionalised and do exactly what their seniors tell them to do. I have to work 'with' the OB a lot and their generic attitude is poor. It's worse at senior level, driven by politics and targets. In London they refer to the 'displacement effect'; a borough will focus on say car crime for 6 weeks and hammer it, regardless of whether arrests are made and prosecutions brought, they are simply displacing the problem to another borough. The neighbouring borough which is focusing on say burglaries does exactly the same, so briefly you'll see a dip in car crime but an increase in burglaries as the crims just move around avoiding the cops.
I'm interested in the Plebgate thing, this PC Wallace is going to be a proper scapegoat, there's no way he wrote his fake allegation letter without some influence from either his mates or his seniors.
It's sad because the good cops are few and far between, hidden amongst the dross. And even sadder, the good guys often turn into arseholes over time.
I take the point that you get twats in every profession, however the consequence of being a twat in Asda is probably minimal, the consequence of being Atwater in the police is likely to be more profound.
Rant over, next week: Bats. Are they really blind or are they just taking the piss out of me?