I do not believe in banning guns, but wouldn't you agree that there are just some people who shouldn't have them? People who are mentally ill, gangs, etc. Where do you all feel we should draw the line?
And we have laws that state that in most states. If they were enforced, it would help a lot. Being a member of a gang is going to be tough to prove and probably unconstitutional. It would be like trying to make a law that Muslims are not allowed to buy a weapon because some people use the religion as an excuse to kill people in mass. Ain't gonna fly. Groups should not be condemned by individual actions, unless the group supports those actions. Unless the person has a criminal record, or one of the problems below, you are not going to be able to stop them.
Next, Mental Illness.
Mental illness is a major issue in this country, mainly because we've tried to sweep it under the carpet. Kids with behavior issues are now "mainstreamed" into normal classes with delusional educational "professionals" claiming it will cause them to act normal. Instead, they are shunned by many of the kids and become hateful and frustrated. How many times have we read that the shooter "was a loner and considered weird"?
The schools are not allowed to sort kids any more. So the kids with mental conditions are left to simmer and won't show up on a mental health list. Or like the one in Florida, he was on the list.... until he turned 18 then the record was cleared as he was then an adult.
Some are true mental illness, some are just behavior disorders that start at home. They need discipline, the one thing that has been systematically removed from the school system. for years. They need help, the one thing the schools are not allowed to single them out for any more.
As has been pointed out, guns have been around for years. Used to see pickup trucks in the parking lots with gun racks on them where the rifles sat so they could go hunting after school. You could mail order weapons for years with no ID. Very few "mass" killings. What has changed?
My opinion is the mass movement away from the idea presented by Jesus that *all* people have worth, is a great deal of the problem. Political leaders routinely state that anyone that believes different from them are worthless. (Deplorables) and Hollywood has movie they want to release stating that they should be captured and hunted!! And we wonder why these young men act this way!!!
Anyone who is not religious has no guide out there that shows that everyone has worth, no matter what their opinion on something. The masses are taught that anyone who doesn't believe what we do are worthless and don't deserve what they have or even life. Hollywood makes the guys who shoot people look glamorous. And don't get me started on the first person shooter games where these kids learn that shooting problems make them fade away.
Ok, this looks like a Pubby answer already, I've gotten carried away. But you get the idea.