I'm still willing to respond in good nature, but it looks like we're just talking past each other now.  

You've presumed a correlation - that the reason there have been no "mass murders" is because of their buyback program.  From that presumption, evidence can be found to support it.  

People like myself don't make that presumption.  That's the difference.  So until your side is willing to drop its preconceived notions, we're just talking to ourselves.

We say maybe it's the family - no fathers anymore.
We say maybe it's the violent entertainment culture. 
We say maybe it's the mental health system.
We say maybe it's the very idea that we can rely on govt to protect us.
You say no, it's the scary looking guns.

None of those issues can be solved, so each side simply uses them to polarize, and we repeat what they say to ourselves and each other.

The most frustrating part for me is the insistence that it's something that should be turned over to govt.  These horrors are a personal and community issue.  They happen and they're terrible.  But no amount of government is going to prevent another one.   When we depend on govt, we stop paying personal attention, because we FEEL safe.  Feeling safe is good, but it's a substitute for being safe.

"Banning"  any type firearm will not make us safe, but some of us will feel safer, and that's enough to gain their vote.