[pacbard]

> It always irks me that discussion of space debris invariably talks about their high velocity relative to the ground, which is completely meaningless.

It's obviously an issue with point of view, but considering only relative velocity isn't also a solution.

If two spacecrafts are on a close approach trajectory, one of them might need to course correct to fix that. Changing the relative direction might allow them to avoid the collision, but will also change their orbit, leading to other problems down the road (e.g., out of wack apo/periapsis). Fixing the orbit after the close approach will also cost more fuel and/or angular momentum, which is in short supply on most spacecrafts.

I like to think about it like two nascar cars. Sure, if you are driving one, the other cars seem to be almost not moving from your seat, but the spectators see something completely different. Any small change (from the driver's view) in steering can have big effects overall.