Spalling?

I have a question about "spalling", as in "space junk is a huge problem
because it is in orbit; and it self amplifies due to a process called
spalling." I agree "Very little natural
debris will be in orbit... " but if one piece of orbiting material hits
another, in order for both to stay in orbit don't they have to have very
"tight" trajectories in both directions and speed coming out of the
collision to stay in orbit? I would think after the collision, assume no
new pieces just to make this simple, both would likely be in orbits which
would take them into the atmosphere within an orbit, and so they would soon
be gone. Thus collisions between orbiting debris should help clean out the
debris. Multiple pieces coming out could well leave a few much smaller
pieces in orbit, but the most of the mass would drop out of orbit from
aerobraking after a single collision. I know there was a video broadcast (I
believe on FOX) on this, but I think this like "beaming people" on star
trek, not taken seriously by scientist. Sincerely, Jay Huebner at
jhuebn@...