I hate this argument, that criminal people sonehow have the ability to do anything anywhere unhindered by everything, and so making laws will only cause more crimes. It is the same type of thinking when people say "masks don't work", 90% efficacy is WORTH HAVING.

It is asinine. Making laws and properly enforcing them would absolutely reduce mass shootings. Some people certainly could still purchase unregistered guns illegally, but it would be a small fraction of the people who would/will do it under our current laws.