Obviously people can enter or leave the planet as long as they're willing to take a risk of dying equal to [space covered by 100s random orbits] / [total surfac

Obviously people can enter or leave the planet as long as they're willing to take a risk of dying equal to [space covered by 100s random orbits] / [total surface of planet], which is nonzero but small. If you're launching straight up, thousands of such asteroids would leave you with 99% chance of success - the trouble is that with modern standards we generally don't consider 99% good enough - e.g. for space shuttle, 2 out of 135 crashed, getting almost 99%, and that's considered not ok; but if you really need to (as opposed to launches just for PR and science) then you can definitely get out of planet 90%+ of the time.