Ask Lemmygrad

In a lot of previous trek shows, the federation is occasionally under siege, but its nearly always depicted as a simple "good vs evil" trope, and the federation never has to get it hands dirty, or do morally questionable things. For the most part, the federation is just peacefully exploring the galaxy, and enjoying paradise.

But that's not how things usually are: we know from experience that socialism is always under siege / under attack from imperialist powers, and as a response they have to develop armies and war industries, intelligence services, cultivate alliances, move populations, and practice realpolitik. Deep space nine forces its characters to encounter these moral conundrums, and we empathize with them. Its easy to be a saint in paradise, but its much more difficult to live in the real world of moral ambiguity where protecting your people is the most important thing.