"Space," it says, "is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is. I mean you may think it's a long way down the road to the chemist, but that's just peanuts to space" -Douglas Adams

I'm not sure if I buy this "earth orbit will be dangerously crowded with debris" business there is a LOT of room up there, the volume of space we are discussing is bigger then the volume of earth, and even if there is a high density of debris most of it is small bits of metal at orbital velocities, which would likely cause similar danger to micrometeorites: which are an engineering problem we need to solve anyway (the whole pray it does not hit anything that goes boom and throw a patch over it fast plan is not acceptable)

The problem is that collisions between larger pieces of debris can generate smaller pieces, more collisions, etc ... the potential for a chain reaction should not be dismissed so lighly because the consequences of humanity not being able to get into space are pretty far-reaching.