From the functional side of things, a semi automatic rifle is even more dangerous than an automatic one, since semi-auto is the shooting mode trained soldiers use to kill as effectively as possible.
Well, then, what would you suggest as a solution to this problem, and the related problem of rampant shootings in cities with pistols? We can say "we should fix the conditions which give rise to violence" but how, and in the meantime, what would you do to try to reduce the damage and deaths from shootings? (Ignore suicides or not, it's up to you)
The solution is pretty simple, i think. a complete ban on sales of non-hunting rifles. This brings back my previous take on this debate which i didn't care to reply to, since i got a rather rude response, but no, an M16 variant is not a hunting weapon, even though you can hunt with it, just like i can hunt with an FN Minimi or Negev LMG.
Since i can't imagine ordinary people with an M24 (Remington 700) killing 50 people in a night club, i'd say those types are relatively more reasonable weapons to sell to civilians who wish to hunt (Although if you already asked for my opinion then hunting for sport should be made completely illegal even before banning weapon sales).
As for handguns, well, the case for self defense is a somewhat reasonable one. i'd say a couple of months waiting period, periodic psychological evaluations, clear criminal records and mandatory training every half a year could suffice. it probably wont stop gun violence casualties completely, but it might somewhat reduce it.