I don't think the Police Union -in and of itself- has gone wrong. It is there after all to fight for and on behalf of it's members to the best of it's ability. It's somewhat like blaming a criminal lawyer fighting on behalf of a defendant.

The problem is that the political and justice system have taken a very pro police stance and this can be seen in many different ways like from "afraid for my life" memes, asset forfeiture issues to the "not clearly established" get out of gaol card to be played at every police trial.

And so there are multiple problems to be looked at. Political candidates are blamed at being "soft on crime" at the slightest hint of pushback, police investigating themselves with no independent oversight , police and prosecutors being on the same "side" against the war on crime - not independent, mixing and conflating the police being a profession ( i.e. a job) with their legal duties . . . and many others besides

All of which have been heavily exploited by the unions - and of course they do. That's their job