I always sided with the Maquis and never understood why the Federation were such pussies with the Cardassians. From what we saw Starfleet was more mature, richer and had more resources and powerful ships than the Cardassians...and yet they negotiate a fairly unfavorable treaty. Perhaps it was a mistake making the Cardassians out to be fairly weak in the early TNG episodes in which they appeared.
I personally supported the Maquis.
Don't forget that a dozen or more Federation colonies were handed over to the Cardassians, but the Cardassians had to hand over about the same number of their colonies. All of this as part of border/territory changes from the peace treaty. In an absolutetist sence the Federation didn't really lose anything and thus the treaty isn't unfair, plus they get peace. In that sense the treaty is perfect.
Only problem was many of the Federation colonists didn't want to leave their homes, thus exposing the flaw in the treaty. But looking at it from a strategic point of view, and TheGodBen alluded to this here, a few lost colonies is better than war right across the Federation/Cardassian border where many more worlds are threatened. Instead of tens of thousands of lives it becomes millions. In that respect the treaty was good for serving the needs of the majority.
Were those colonies 'betrayed' by the Federation? In all honesty yes, just because of some redrawing of the lines on the interplanetary map. Now the flaw in the Maquis strategy of attacking the Cardassians was that it would mean serious trouble for the colonies in Cardassian space. A bad situation would just get worst, the Cardassians were just looking for an excuse to exercise their brutal police state policies on those colonies, and that's what the Maquis gave them.
And then the Cardassians could claim they were maintaining 'law and order', and then pressurize the Federation into sorting out the mess to keep the peace treaty from being ripped to shreds. By attacking the Cardassians, the Maquis lost their only ally; the Federation.
Also as Sisko said to Eddington (some years later as the Maquis situation developed):
You know what I see out there, Mister Eddington? I see victims... But not of Cardassia or the Federation. Victims of you. The Maquis. You've sold these people the dream that one day, they can go back to those farms and homes and schools -- but you know they never can. And the longer you keep that hope alive, the longer they're going to suffer.