Sure, if the AR-15 or any assault weapon were made illegal there would undoubtedly be a black market for criminals to obtain the guns anyways. That doesn't mean it wouldn't at least reduce the risk of a criminal obtaining a highly destructive rifle.
Raising the legal age to 21 would have prevented Nikolas Cruz from personally buying a gun. If assault weapons were banned period, i am doubtful he would have access to a weapons black market (as a mentally deranged high schooler).
I also disagree with your hypothetical, in that I don't think there should be, or are any "good guys" with guns- outside of people hired for security/the police. The notion of arming more people in public areas and facilities is not intelligent- you don't necessarily have to be mentally ill to get angry enough to pull the trigger. People who own guns should go through strict training (and potentially licensing) that requires clear evidence of responsible gun ownership.
Also, I don't think the march for our lives movement is as willfully ignorant as many believe.. there are many smart kids who can see past our distorted view of how we must think about guns.
If there is anything that comes with this movement, I support delegitimizing all of the congressmen who are NRA puppets... the NRA has had a huge grip on congress for decades now. I am more indifferent on which weapons to ban and more interested in bringing down the gun lobby.
I think any responsible gun owner can see there needs to be some degree of further regulation, required training and background checks when it comes to guns. The fact I can go to a gun show and purchase a high capacity mag AR with minimal difficulty scares me. We spend years training kids to drive, we created strict boundaries and laws for driving and ultimately driving has become safer. I want the same to occur with guns.
I've pushed my response over to a new thread if you
are interested in picking up where we had left off at.Thanks again for sharing your thoughts @studgriffin.