So mass shooters can just reload, but not defenders. You are too funny today.
A defender may be wounded at the start of a fight.....and if they have to change a magazine simply because stupid people like you don't like 30 round magazines...it may put their lives at risk...their small motor skills may be affected by adrenaline or they may only have the use of one arm....like the federal agent in the Miami Bank Robbery shootout.....
So having a large capacity magazine aids the innocent defender but makes no difference to the mass shooter...who goes to a gun free zone to murder unarmed people....and has no need to worry about return fire....since they either kill themselves or surrender as soon as they face armed resistance....