I really don't expect to change any minds. Attitudes today are well entrenched but nevertheless I think the question is worth asking.
Despite the demonization of firearms and the AR-15 rifle in particular by many these days an indisputable fact remains. The AR-15 rifle has not fundamentally changed since it's introduction to the civilian market in the 1960s. Ergonomics have changed somewhat but it has not somehow become a more deadly weapon than it ever was. Nevertheless, you could mail order one with no background check yet the AR was in civilian hands for 40 years before one was ever used in a mass shooting. You cannot attribute mass shootings to the design of the rifle itself or we would have been seeing these shootings decades before we actually did. That begs the question, if the AR-15 has not fundamentally changed (and by extension the semi-automatic firearms which have been around equally as long, if not longer) then what has changed to make mass shootings so common?