Not sure if you are being sarcastic or not, but there have been semi auto pistols/rifles since before America was founded. If you weren't being sarcastic then please accept my apologies up front :)

Mass shootings almost never happened up until the last 30 years(and really they still almost never happen), as culture continues to rot there will be more. Even so the amount of people who die in them is very low compared to almost any other cause of death. More people fall out of bed each year and die than mass shootings by like 20x.

https://time.com/4965022/deadliest-mass-shooting-us-history/

http://mentalfloss.com/article/58235/11-mundane-objects-are-statistically-deadlier-sharks

We aren't heartless, in fact guns save more innocent lives by a factor of almost 75x vs bad guys killing someone. This stat was found by the Clinton Administration study. It is statistically better for more people to have guns.

https://steemit.com/informationwar/@truthforce/gun-statistics-let-s-talk-facts-logic-context-epidsode-1

@truthforce writing