Why people are so nice on Second Life (and not-so much on the subway)

Thinking about the infinite nature of hyper-reality, I considered this: the more people join SL the more diverse and interesting the community. Not so in RL. Overpopulation is a real issue. We are running out of space. It's hard to be friendly and accepting of every bumbling grad-student with stars in his eyes from Oregon, when you're already on an overstuffed 9AM subway. New York, like SL has enough to do to keep you busy for a theoretical life-time, but unlike SL, it could potentially become to crowded to live comfortably. Second-life will never experience this. As we continue to grow at an astronomical rate (ever look at a chart of the projected population in 50 years? 100?), tensions will mount and we will need some place accepting and infinite to hang-out. Any ideas?