I agree with you and everyone else that it's a terrible idea to keep changing the films. I mean, no shit; is there anyone saying it's a GOOD idea?
I agree that it's ironic that somebody who fought so hard against the colorization of films is now addicted to repeatedly altering his OWN films. As I did when South Park made that point a decade ago.
However, editing your own films isn't PRECISELY the same thing as buying up the rights to a bunch of other people's films and editing THEM. Lucas's position may be ironic, but it's not logically inconsistent. (Except, I suppose, in the case of Empire, which he did not direct.)
Legally, of course both those things are permissible. Ethically, well, ethics are personal and subjective; I'd argue that it would be best to leave old shit alone but that it's more ethical to hack your own shit up than somebody else's. Financially? Well, maybe he'll quit doing it if people quit buying the goddamn things.