Whether or not you personally remember semi-autos back in the day is irrelevant.  They were there, and they were very easily obtainable by anyone who wanted to go on a shooting rampage.  But, not many wanted to go on shooting rampages back then.  

That pretty clearly spells out this is not a gun issue.  It's a mental health issue, it's a societal issue, but it's not a gun issue because the guns have always been there.