First off, no one was beaten up. He was struck several times because he refused multiple times to comply with a lawful police request for him to allow himself to be arrested. 
There is no history of the police downtown doing anything of the sort. Have you been downtown in the past several years, anywhere between the library and Broadway? At night? It has become an area where homeless and violent folks who use them as shields to hang out. I'm not talking 8 or 10. I'm talking 30, 40, 50. On just about every corner, making it hard for folks to walk on the sidewalks. More than a few have dogs that also block the way. 
I suggest you visit Salem, Bend, Corvallis, and even Portland: nowhere in the recreational areas of the city will you see such amazing numbers of vagrants/aggressive guys (it's primarily a male crowd, overwhelmingly so). 
Why you and others persist as seeing these folks as victims is beyond me.