southeastshooter,
Respectfully, you have already lost the debate. Your professor has already framed the debate by insinuating that guns should be banned unless it can be proven that their mere presence reduces overall crime. I submit that you should not engage in his game, but instead pose to him the concept that guns do not affect crime rates at all, but merely empower the individual to protect himself, instead of relying solely on the authorities for protection. Any objections to this notion on his part will likely be due to some vague idea that guns are unsafe in the hands of the untrained, unwashed proletariat. Simply counter with the fact that freedom is not, and has never been, guaranteed safe.