I think there's more to it than actively opposing - in Ireland deaths at the hands of the cops are rare, and there's a huge fuss when one happens ... but that's more a manifestation of the norms of Irish society than anything to do with active opposition to police brutality. It's more - if police brutality is rare then there's not much point in becoming a cop if you're a brute
This mechanism reinforces the societal norms that created it, like many others. If the Irish didn't intensely oppose police brutality, more brutes would enter the police force, leading to higher incentives for brutes to join the force. It looks like a self-amplifying loop but it works towards society's demands.
