Semiauto guns have been around over 100 years. Yet mass shootings (not mob related) are a fairly recent thing. Why? The answer is how we deal with those with mental health issues. In the past they were put in institutions. That no longer occurs.
So continue with the knee jerk reaction re guns. That is not the issue. And the reality is, even if there was no 2nd Amendment and they could be banned by a simple law passed by Congress, such an effort would be a failure, like prohibition and the "war on drugs". We have two large, essentially open borders to our north and south, and two huge coastlines. There would be no way to keep them out.
And re gun laws. CT has some of the most stringent laws. The shooter was not old enough to buy. And schools are "no gun zones". So we have a situation here where we have tough gun laws where this happened.
The key is keeping guns out of the hands of criminals and those with mental health issues. Because those are the guys that use them, no matter what the law says. Blanket gun laws just take guns out of the hands of law abiding citizens.