I'm glad to hear your friend is ok. He wouldn't have been the first person minding their own business and enjoying a night out to have some alcohol-fuelled {bleep}tard knock someone's face to pieces or put a knife in their guts - for no reason whatsoever. I couldn't imagine how bad that would have been.
Some people just can't handle the drink - the alcohol turns them like nasty kids, unreasoning, vindictive, and pitiless. Some people go out looking for a fight for some kind of feeble machismo. Some people can't take the fact that they're lacking something everyone else has and decide just to attack whoever looks the most vulnerable when it spills over in drink-addled rage. Then they attack the medical staff when taken to hospital...
The bars are at least partly to blame though. Nightclubs and bars do their best to sell as much drink in as short a time as possible, in overcrowded places. They build up powder kegs waiting for a spark. Binge drinking is pure evil. It brings out the worst in everyone.