Handguns kill FAR more people than assault rifles. Yes, semi-auto rifles, like the AR-15 have been used in some mass shootings, but usually alongside handguns. Handguns are more easily concealed, and are effective at short range.
Banning semi-auto "assault weapons" won't solve anything. If you take away assault weapons, there are lots of other legal guns. A shotgun in a crowd would be devastating, especially a high magazine shotgun with a choke (to spread the stream of pellets). A 12 gauge 00 shotgun shell holds nine pellets, each the rough size of a .32 caliber bullet. And shotguns don't really even need to be aimed.
If you illegalize all guns these idjits will turn to suicide bombs, fertilizer bombs, arson, cars through crowds, etc. Hell, even flamethrowers are legal to own in the U.S., and Tesla is now making them, and sold $10M worth in 4 days. Can you imagine what a flamethrower could do in a crowd? Ugh.
Unfortunately, I do not see any easy fix. It starts with reasonable restrictions on purchase, required disclosure and cooperation among the States and Fed. to share background information, etc. It continues with investment in better mental health care.
I personally don't care whether guns are legal or not. There are lots of senseless deaths in this country that could be prevented. Alcohol deaths kill more people than guns. If we are for preserving human life, as a country, we are somewhat hypocritical when prohibition cannot be upheld(people need their drinky), and the laws for killing or severely injuring when one drinks and drives is often a slap on the wrist. My Uncle suffered a traumatic brain injury from getting hit from a drunk driver. It left him helpless, and the driver served no jail time, just lost his license for a few months. In California, misdemeanor negligent vehicular manslaughter has a sentence up to one year (other circumstances such as excess speeding, etc., can increase the amount). Max sentence is generally 10 years. Not a lot of punishment for taking a life IMO.
Then there is abortion...
To be quite frank, I don't think a human life is worth much, and based on historical legislation in this country, our leaders tend to agree.