This is a great article on Den of Geek talking about the realistic take DS9 has on the Star Trek universe. One of the things I say on The Orb all the time is that DS9 took the ideals of the Federation and asked what's it mean to really live like this, especially in a universe that does not share those beliefs a lot of the time. This article does a great job of pointing out where DS9 really challenges us to ask the hard questions through it's 7 year run.