"The Federation" didn't engage in genocide at all. Some rogue elements of the Federation society attempted it, (hell, just one guy did if you take my point of view) and still it's not obvious that any one died from the virus. Trying to blow up the Bajoran sun is OK, though. Because the Federation was the aggressor, right? The Founders and the Dominion are poor victims of the terrible Federation's all-mighty conquering armies of Section 31 ninjas, and were justified in their attempt to destroy an entire race, but not the Feds. Nope. Humans are just evil. Basically, both sides tried horrible things to wipe out the other side. But the Federation's side was an unauthorized attempt, while the Dominion's side was authorized and in fact carried out by one of their leaders. Which is worse? Will someone suggest the Bashir impersonator was a rogue changeling the way Sloan was a rogue Federation agent?