Shop window, passerby's head, car - equally good targets for a brick.
I've never heard about passersby's getting injured by an attack by the protesters. Any sources you can cite? There have been many injuries caused by the police to people who were minding their own business, even in their own workplaces.
Even if some 5% of protesters act on a decent cause, the rest of them are what they are: adrenaline junkies, seeking to channel their frustration and violent tendencies.
How did you get that impression? That's the complete opposite of what is really going on. The evidence is out there. I suggest you stop reading your favorite commentaries and begin to collect raw information and interpret for yourself.