It looks like you lost the argument and did youself no favors. You used emotions and loaded phrases. the emotion is emphasised by storming out. This emotional outburst could make you appear like the "extremist" the prof portrayed you as. You should have stuck to logic with arguments such as "the criminals already have guns" or "to think that criminals would suddenly start obeying laws if you made a new gun law is literally crasy". Or use humor "well if somebody wants to kill me, i want to kill them back, and i want to have a bigger gun" etc. also, like 44 amp said, when he said you where like iraq soldiers, remind him you're also like american soldiers. You can only throw out so many canned phrases, think on your feet.
I doubt any of you classmates where swayed towards guns by this argument. some of them either have guns or family members that own guns and you want to be just another student who happens to have a gun(or 10). Not some crazy "extremist" gunman, just another student thinking with his head.
Ess Kay Ess