If drugs are legal, the parallel market for them ceases to exist. If you can buy a drug at a store, a shady dealer doesn’t need to fight for territory with the next guy over. This is a crime that ceases to be committed.

If a guy buys some weed and heads into a crowd, at most he can inconvenience some people with the smell.

If guns are legal and that same guy has a mental issue, that crowd can get shot. This is a crime that can more easily be committed by that legality.

And before armchair experts can come at me, just look at every other country where guns are not legal, and measure the amount of gun violence compared to that one where they are.