You miss a point about symbolic gestures. It is a cultural ploy for the long term de-legitimization of that part of the gun world. Folks who are new to the argument, as new generations come along, will say that these must be a priori bad as they are banned. It is similar to banning smoking. Yes, folks smoke but they are seen as pariahs.
I think a lot of it is symbolic. WE HAVE TO DO SOMETHING, EVEN IF IT ONLY SAVES ONE LIFE IT'S WORTHWHILE!... If you own no guns, haven't ever shot a gun, have no interest in guns a 10 round limit will seem reasonable if not excessively lenient. Many lawmakers figure attacking gun rights is a winning proposition for them and banning 10 round magazines is seen as a good first step.