Ro's decision is understandable if you consider her life experiences.

The Maquis are not created in universe to be good or bad. They are not black or white, they are gray all the way. Because that's how all freedom fighters/terrorists are in their time. They get their marks from history. Some upstart colonists in the 1770s tend to get a more favorable score from history. For the communists in Cuba it depends who you ask.

Reality is a clusterfuck and politics is the art of what's possible. No one designed the situation to place colonists on these planets, to have a war in the neighborhood, and then have to come up with a compromise to end the killing. It happened and now they have to deal with it. I'd like to see the SWOT analysis of each colonized planet, just to see if they considered risking setting off the stereotypical fascist race in the neighborhood by their presence. That is to say the colonists may not be entirely blameless either. But regardless, the federation made an agreement to end the killing in a big war. They drew a line on a map and that's never not caused other problems in history. In the middle east, in Korea, in Europe, etc. It's often the best solution to end or prevent the fighting but it's still a shit solution that doesn't solve all problems. Indeed, one might argue it may only be a temporary reprieve. So the Maquis are borne out of gray, they do things that are gray, often more on the darker spectrum, and then the authorities come in and also react in dark gray when they poison an entire planet's atmosphere. The writers even threw in some native American tribes having to relocate or accept Cardassian rule to perfect the clusterfuck.

The way some of the Maquis stories are told in late TNG and then DS9 is not the best Trek has to offer. But if you zoom out, the overall situation they've created is realistic and believable. The Maquis are ambiguous, the role of the federation is ambiguous. It's all just gray. And while I don't think it's super unrealistic that they just get wiped out by the Ketracel White addicts, I thought it's a lazy writers' end to a great scenario they had created.