I don't in any way excuse his actions on the show (the "Dukat did nothing wrong" crowd actually morphed into the alt-right over time from what I gathered). But it's simply not fitting within the Trek message to argue that there are pure villains which are beyond redemption. Not only that, but heel-face turn makes for a great story. It's part of why people love Jaime Lannister's arc in Game of Thrones (which is even more explicit in the books). He slowly morphs from someone contemptible into someone complicated, and finally into someone genuinely heroic.
Dukat is one of the better characters the franchise ever portrayed. It's ironic that he wasn't even a "main" character...
I agree with you both; but I think not everyone needs to be redeemed - and I think it's worth considering that his villainy is important too. As I said Dukat is charismatic even at his worst - but he's far worse than Jaime Lannister, he's Tywin instead. We want people to be nice, to be heroes or have redemptive sagas - but why should we? Dukat's complications and flawed self-perceptions, as well as his evil acts/decisions, as well as that of many Cardassians (Garak, Tain, Damar, Ghemor, etc), are what make them such a
brilliant collection to watch and read about.
Also have you read Una McCormack's
Never-Ending Sacrifice or
Crimson Shadow? I know some people scoff at tie-in lit (although I think that is silly), but McCormack has been a judge on the Arthur C Clarke prize, is very well regarded in UK science fiction writing, has a phd in sociology from Cambridge Uni and teaches creative writing.... She's also a brilliant writer on Cardassian society, following on from Robinson himself (her earliest novel,
The Lotus Flower, follows on well from his
A Stitch in Time, as well as much of what you have both, and others have, written).
Heck, through
Stitch Robinson doesn't have Garak really learn the true errors of his society until really after the series ended, when he's compiling his memoirs and debating what political faction he might endorse. Both it and McCormack's works show this - definitely if you can, read
Stitch,
Lotus Flower,
Never-Ending Sacrifice and
Crimson Shadow. They are beautiful, especially
NES and
CS.