I wouldn't support a ban on guns, but your claim that large clips keeps America safe from the government is total laughable. That was true when the weapons of the military were the same as the weapons of the people, but that hasn't been true for at least 100 years. even if you could legally buy a F16, you couldn't afford it, much less fly it. Maybe it's just me, but I'm perfectly fine with not letting people own nukes, grenades, tanks and so on.
The erosion of the 4th amendment over the last 40 years is far greater than the 2nd.
How about this argument? If a few criminals with guns were invading my home, I'd sure as hell like to have more than 10 rounds which with to defend my family? I'm not a bad shot, but I don't get to the range weekly like I once did, and I don't expect a criminal threatening my family would stand still like a paper target does on the range. Nor would I want to face armed criminals standing out in the open in a good shooter's stance.
What that means is that I would expect that I would miss, and that even my hits very well might not be disabling wounds.
Extra magazines help, but the criminals are more likely to be prepared well than the victims, and it's not like you want to be fumbling around in the dark for magazines before running to check if your kids are ok.
A criminal intent on mass murder will likely bring along lots of extra magazines, and it doesn't take long to change them out with practice. Even if the slide locks back they would be able to reload before their victims will have a chance to realize a reload is needed and take even a couple steps. The people most likely to be effected by magazine size restrictions are law abiding citizens, not criminals.