Criminals are going to find a way to get guns anyways, so we might as well make it as easy as possible for them?
Yes, people who want to do something bad can find a way to do it, but society can also try to make it difficult or somewhat ineffective for them to take the steps to do it.
I also eagerly await the story where a mass shooter is pre-emptively taken out by a law abiding citizen who is carrying a legal firearm and becomes Rambo at the precise instant the killer is going to fly off the handle, and saves the day. That's going to be a huge victory for the pro gun side of the debate.