I don't think its being disingenuous. Simon asserted that rights are not absolute (in general I agree by the way). The question is, does that apply to all rights? Any attempt to place any restriction on abortion is quickly turned into a fight over a fundamental right. Yet pretty much the same people think other rights can be restricted. Which is it? My question is theoretical , as with gun ownership, the Supreme Court has spoken.
Back to the main topic, here's some interesting numbers. Out of 12,000 plus murders per year, rifles are used in about 300. I don't see that an assault weapon ban will move those numbers by very much.
https://www.fbi.gov/about-us/cjis/ucr/crime-in-the-u.s/2012/crime-in-the-u.s.-2012/offenses-known-to-law-enforcement/expanded-homicide/expanded_homicide_data_table_8_murder_victims_by_weapon_2008-2012.xls
Also from what's on CNN right now, this is looking more and more like a terrorist attack, not a work place shooting. They had bombs and thousands of rounds of ammo in their house.
Also I'm hearing rumors that they purchased the guns legally in California, which has some really strict gun laws, including an assault weapons ban. I haven't been able to confirm if they did fact buy the guns in CA.
PS I do not currently own a gun.