I admit, it's grand notion... to resign from a category when you get higher permissions, or if you aren't as active in the cat as you once were, to entice new editors who might be hesitant to apply where another editor is listed. And, we're encouraged to do just that. However, in practice, it just doesn't seem to make that big a difference. In my time as an editor, I've resigned from a dozen or more cats, and not one of them has been picked up by another editor. There are just so many categories in the ODP, that a few editors hoarding cats just doesn't affect the overall picture much.
It's certainly far from "ruining the ODP".
I sometimes feel sorry for my little orphaned cats... they must feel so abandoned... <img src="/images/icons/smile.gif" alt="" />