The more people you arm the more crazy people you arm. You might increase the odds in some cases someone thwarts a crime or saves lives,
but the other hand you might increase the odds that when some nut goes over the edge, the fact that he already has easily obtainable weapons might make the consequences worse.
I hate to point out the obvious but laws regulate those who will follow the law. Committing murder is breaking the biggest law there is. What makes you think that someone who wishes to commit murder is going to follow your pesky little gun law?
laws DISARM good people...they don't take guns away from bad people. When will you ever learn that simple basic fact.