And you're operating under the false assumption that the Federation was doing -anything- to stop this. Picard, Sisko and Necheyev all said they're on the Cardassian side of the DMZ, they're on their own when pressed on the issue. When Sisko asked Husdon about taking it to the Cardassian authorities..
HUDSON (overlapping) Enforcing the laws? The Cardassian "authorities" were part of a mob that stoned two of our colonists on the streets of Ropal City three days ago...
So don't tell me the Cardassians were interested in peace. They weren't. Before the treaty was even negotiated they tried to seize Minos Korva. Even after it they'd attack Federation ships(like in the Chase) when convenient. They routinely terrorized the colonists, and were arming for a new conflict with the Federation.
The Federation went after the wrong people all in the name of peace with the Cardassians. Which yeah... that worked out real well. The Cardassians only instigated the largest war in the history of the Federation a few years later.