Your ethics don't do you much good if you cease to exist as a society. Federation historians and philosophers may look unfavorably on Sisko's actions, but they'll be able to pass those judgements in a free society because of those same actions.
True-I'd rather have the Federation around than any of the other two powers.
Not that many fans wasted any tears over them being tricked into it. The Romulans were very short sighted. Being a-holes didn't make it any harder.
The Federation/Starfleet knew all about their plan and gave Sisko their blessing. This is higher up people we're talking about.
But there's the issue of refusing aid to cultures who are fighting for freedom, like the Bajorans, and then have 'righteous anger' when another power refuses to help them when they might lose theirs.
Romulans, hate them or not, were exercising their sovereign right not to interfere in the war. Technically that would be an internal matter.
It's a subtle theme you can see in some episodes.
Janeway gets mad when another culture wouldn't share their travel technology that would get them home much faster.
Picard got mad when a time traveler from the future wouldn't tell them what was going to happen with their mission to save a planetary disaster.
Interestingly some of his own crew were on the planet .