No it's not silly. And most gun owners, even those with "assault weapons", whatever the hell that actually means, are law abiding citizens who do not start bloody rampages.
I honestly believe that regulation will not impact the miniscule percentage of rampages in a statistically significant way. Arguing regulation doesn't make sense to me, because this will not stop "crazy", which is the root cause of this problem. Not the guns. If a person is bound and determined to eliminate innocent people, they will find a way to do it.
I guess no one is arguing that we should repeal the 2nd, which is good, because that has about as much chance of happening as me getting a date with Megan Fox. As far as your bolded statement above, yes, you could reduce the risk, but the amount of people killed in "fun feuled massacres" is so minutely small already that I do not believe it is worth infringing on peoples rights to eliminate them. There are much, MUCH bigger killers out there that would do more people more good to focus on...