I've never really liked that reasoning. If that's the case, then right-handed people should be playing "left-handed" guitars, with their right hands doing the fretting.

Personally, fretting with my left hand just doesn't feel natural. When I first got interested in playing, I asked a salesman at a Guitar Center about left-handed instruments. He handed me a standard guitar, and showed me the fingering for a G chord. It was uncomfortable, but that's obviously expected for the first time I'd ever held a guitar. However, when I flipped it around and fretted with my right hand, it felt much more natural. So ever since, I've played left-handed.