That is the real point of how brilliant they were. No matter how bad they got they could trick you (both characters and audience) into liking them in the end. Dukat and Damar both done it and we really should not like Garak either but they were all compelling and nuancedDukat was the best villain in Star Trek!
And the Cardassians were the perfect "bad guys", much better than the Borg. They didn't have super powers or superior technology or weren't inhuman killing machines. Instead they were cunning, smart, violent and unreliable.
And at the end of the series, I cheered for them when they fought the genocidial Dominion!