1. Space is really big so the odds of anything hitting each other are low. 2. They are launching their initial satellites in extremely low earth orbit such t

1. Space is really big so the odds of anything hitting each other are low. 2. They are launching their initial satellites in extremely low earth orbit such that atmospheric drag will cause them to decay and burn up in the atmosphere within 5 years. They are also attempting to design their satellites such that every single part of them will burn up in the atmosphere so that there is no risk of any piece hitting someone. 3. The US government is also concerned about this which is why spacex is doing their initial launch into a lower orbit that guarantees their decay into the atmosphere. Their future launches into higher orbits with longer decays will have extra considerations for such problem and thus will be evaluated by the US government individually so I would not be too worried.