The Dominion War brought out the worst in Starfleet, but it's no different than essentially every war fought by anyone ever. The Cardassian War brought out the worst in Robert Maxwell. Old antagonisms against the Klingons brought out racism in Kirk. Shadows of the Romulan War impeded the crew in Balance of Terror. Just as war is important, in each and every single example, is how our heroes regain their humanity after that.
During the 1990's, it was a time dealing with the problems with subjects like war. Recall, Deep Space 9 was a dark side of what history can give us. If Deep Space 9 did not have a war, I think the show would have ended around the third season.