When I lived in The Basque Country I was teaching a very senior politician who over various classes concluded with me that 'You have a young person who is attracted by some military discipline but not too much, a clear-cut political stance, a sense of belonging to an organisation with its uniform and its customs and secrets, the chance for physical violence, a clear-cut enemy, the workmates are the social life, being able to walk down the street out of their role and people not know their secret life and so on and on'.
He was making the point that in the Basque Country young people, often very similar people from similar backgrounds, ended up on one side or the other of photos like this one
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It's not exactly like that in the UK but there is the at-present insurmountable problem that a great many of the attractions of policing the country appeal to too many wrong'uns from the off or to people who end up corrupted.
As Plato didn't say 'The last people you want in the police are people who want to be there'. I see no easy solution.