And a gun. A gun is really an important part of this, and the bit that we can have some control over, and a gun is the thing that makes this situation different in the US rather than UK or Australia.
It isn't like we are going to get rid of drinking locations. If they weren't happening in public, they'd happen at people's houses. Same with alcohol - we've tried it. I won't speculate on possible drugs since we aren't quite sure about that bit, but it is unlikely we'll get rid of these things either.
Without the gun, the weapons likely wouldn't have been so deadly especially if the person doesn't have proper training and control. Most likely, the weapons would be things like knives or broken bottles. Not saying they aren't deadly, just that they take a bit more work and might have more chance to live.
Now I'll assume the weapon was illegal. Hey, it happens even in place with tough laws. If they are put in place correctly (see Australia, who had a similar gun culture to the US for an example), fewer people have guns. Illegal guns are harder to come by because of that. Between scarcity and increased risk in selling, prices will likely go up and the end result is that fewer criminals actually have guns because fewer criminals can afford them. Especially possible low-level drug dealers.