I am in no way comparing the Cardassians to the KKK. The KKK is just a semi-organized group of racist red necks that like to play dress up, drink, and hate on non-whites. The Cardassians had an actual cause for enslaving the Bajorans that was not based on hatred. They saw an inferior race and they took it upon themselves to subject and enlighten them. If there is any hatred towards the Bajorans now it is only because it reminds them of their own weakness of not being able to occupy Bajor for longer than 50 years. The free Bajoran is just a reminder of that weakness.
I think it is nonsense that the idea that enslaving and subjugating an entire species to "enlighten" them is an acceptable practice. The Cardassians did what they did because they had the strength to do it so they could benefit their empire by strip mining the planet and using the population to do the work. At no point did they treat the Bajorans with respect or any sense of equality.
The Cardassians committed massacres before they left. Then as they were leaving they poisoned land to create famine and starvation amongst the Bajorans. They supported an attempted coup against the government. They kidnapped and tortured people from Bajor, forces women (and probably men) into prostitution, they stole religious artefacts and resources. I find it next to impossible to believe that the quality of life of the Bajorans got better due to Cardassian occupation.