Of course it's shit that he got beat up for only being drunk.
The point is that it isn't about what's right, it's about shitty people in the world that want to and will fuck you up in every possible way if they get the chance. This happened to OP as he said
If you walk into the most ghetto place ever with your camera on your neck and looking like a tourist you will get fucked up(never done that, but it probably has happened). Nobody wants to get the shit beat out of them and get robbed but that's just how some places in the world are.
You can't reason with everyone. The Croatian cop was a piece of shit, nobody is denying that. But just realise that in some countries people will hurt you really bad for only a hundred bucks that they can steal from you.
OP didn't deserve to get beaten up and robbed but he made a dumb decision of being drunk and having the bad luck af meeting a corrupt cop. By being fucking drunk in a foreign country all by himself "maximised" the chance of this happening.