Stripping Cardassia of ill-gained colonial possessions sounds fine and well, until one thinks what it actually means. Millions of innocents are going to be deported, their colonial lives replaced by ones of misery on some concentration camp or another until enough have died so that they can be resettled on the former homeworld in those horrid pre-conquest conditions. Or then all-new worlds are going to be allocated for the innocents, meaning Cardassia just swaps conquests.
Timo Saloniemi
You're assuming the Cardassians were actually colonizing all the worlds they conquered. Fifty years of occupation on Bajor didn't seem to involve much of anything in the way of colonization - just military dictatorship. Part of me suspects the Cardassian paramilitary 'colonists' in the demilitarized zone were nothing more than a convenient political ploy to make Federation citizens (and politicians) less inclined to support the war effort. The Cardassians may not have bothered with that sort of thing at all if they were facing any other (less morally relativistic) enemy.
Also, we're talking about civilizations that span millions of light years. Deportation doesn't automatically have to end up in 'concentration camps'. They could potentially have an entire (otherwise uninhabited) world to themselves. It probably wouldn't be the best world ever (or else someone else would be there already) but with the inevitable Federation donations of colonization technology, it would probably be a perfectly reasonable existence.