- "We need to avoid what I call super-spreader events. When these things explode or something collides with them, it generates thousands of pieces of debris that then become a hazard to something else that we care about."
There was one of these just a couple weeks ago (and that was not the first),
Yes, because the bits that come off satellites don't stay in a perfect orbit with them - inclination and other orbital elements may change, which means they may eventually collide with other satellites.
Actually GEO is one of the worse orbits for this, because
1) unlike LEO, there's so little drag that both large particles and small fragments are essentially up there forever
2) all the satellites are concentrated in a line, not spread out in a 2D plane or (even better) a 3D volume (collisional probability scales as number density squared)
3) despite that, the moon perturbs any uncontrolled debris into a slightly inclined orbit that nevertheless crosses GEO with >500 m/s relative velocity
If you want to intentionally rendezvous with and deorbit satellite debris, GEO is certainly one of the orbits to prioritize.
There was one of these just a couple weeks ago (and that was not the first),
https://news.ycombinator.com/item?id=41904346 ("Intelsat 33e breaks up in geostationary orbit")