The problem is that, despite what most think, being stuck in first person is rather unrealistic, as it completely cuts off your peripheral vision. I dunno about you, but I can see more than the 70 some-odd degrees directly in front of me. On top of that, we have the ability to 'sense' things around us via our other senses. While it may sound realistic to be limited to first person alone, it would actually remove an element of such. (This is part of the reason why melee is so much harder in first person, as you can't see the environment around you, or often the guy you're fighting.)
