DS9 does a good job with episodes like Cardassians because of how the writers view the morality of the characters in a more realistic way. Where as the TOS and TNG viewed people in the 23rd and 24th century as having become almost innately better people, the writers of DS9 treats it as much more of a cultural influence. That's why we get tons of speeches from Kirk and Picard talking about how humans have evolved to become more civilized and rational as if humans somehow gained extra morality and logic genes between the 21st and 23rd/24th century and that the Federation was formed because human brains have become biologically superior. The characters represent something that we can strive for but never achieve because we simply aren't "evolved" enough. It's also why some people claim that DS9 betrayed Roddenberry's vision by making Star Trek "darker."
However, in reality, DS9 simply interprets Roddenberry's vision differently. DS9 treats humans like they're still humans, with all the strengths and weaknesses that we've always had. The DS9 writers sees that the reason why humans have become better is because the culture they embraced has allowed them to expand their potential. However, since humans are still humans and all the things that have made them in the 24th century better is due to culture then when people are taken out of that culture, we get to see that they're really not that different from us. That also means that the ideals and principles of the Federation are not beyond our reach. It is possible for us to become like the more "evolved" people of the 24th century by improving our culture and society.
By extension, the same concept can be expanded to other species as we see in an episode like Cardassians. We see that what truly separates us from other people is not something immutable like biology but culture. The Cardassians are not innately hostile or evil but live under a society that indoctrinates its citizens. The bad guy therefore is not the species but the social construct under which they are ruled.
However, in reality, DS9 simply interprets Roddenberry's vision differently. DS9 treats humans like they're still humans, with all the strengths and weaknesses that we've always had. The DS9 writers sees that the reason why humans have become better is because the culture they embraced has allowed them to expand their potential. However, since humans are still humans and all the things that have made them in the 24th century better is due to culture then when people are taken out of that culture, we get to see that they're really not that different from us. That also means that the ideals and principles of the Federation are not beyond our reach. It is possible for us to become like the more "evolved" people of the 24th century by improving our culture and society.
By extension, the same concept can be expanded to other species as we see in an episode like Cardassians. We see that what truly separates us from other people is not something immutable like biology but culture. The Cardassians are not innately hostile or evil but live under a society that indoctrinates its citizens. The bad guy therefore is not the species but the social construct under which they are ruled.
), "Rules of Acquisition" was a bit of a hit and miss ( there were some funny bits in it, but when the Ferengi woman threw herself at Quark I was cringing 
)
, and Will Riker and 
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