"...If the public were not allowed to use guns, then there would be less guns on the streets, and therefore less shootings..."
Well, you have made an assumption there, mdma:
That the gun used in the shooting was legally held by an individual, either the shooter himself, or an individual from which the shooter 'acquired' the gun.
"...I ask you, which is more dangerous, Heroin or a loaded gun in the hands of a nutcase?..."
That's not a relevant statement at all. I could say what's more dangerous, a scalpel in the hands of a doctor who is off his rocker, or a doped up pilot at the controls of a Cessna?
These comparisons aren't useful.
What will be useful is to find out a bit more about this case:
1) Whose gun was it?
2) How did the assailant get the gun?
3) Was any attempt made by the organisers of the gig to make sure that weapons were not brought onto the premises?
In SA I frequently have to put up with the inconvenience of being scanned with a Garrett wand upon entering certain premises, including bars and casinos. I have to hand over my gun and it gets locked in a safe. This even happened at a scrap yard when I went looking for a dash component for my old Ford.
Even when entering banks, I still get scanned even though I can't possibly get any money from the staff, or hurt them behind the glass. The guard still scans me and demands ID and gun license before he lets me in.
Maybe what you want is better control over people going to these gigs with regards to weapons. There isn't any reason for someone to have weapons at a gig.