They're willing to risk a war between the Federation and the Cardassians for property rights in a galaxy where there seems to be plenty of habitable planets to choose from.
As was often the case with DS9 and occasionally TNG they are trying to introduce scarcity and economics into a system that we were assured has neither.
Going back to Sisco's line about it being easy to be a saint in paradise, WHY did these people leave paradise? Was there no room?
The one piece that is never explained that could give the viewers a reasonable take on the people who live on these planets: Why HERE? Why is it THIS land?
Give me an answer to that and I can say they should tell the Cardassians to go pound sand.
Regarding the Maquis...
The Federation told those colonists decades ago that where they were settling was a 'hotly disputed' region. (Admiral Nechayev said this.)
"Disputed" means there's a dispute. If the Federation wasn't disputing it then it would just have been Cardassian space. SOMEONE in the Federation had the impression that it belonged to the Federation.
If your neighbor decides that half of your lawn belongs to them then it could be said that it is "disputed". And if you do anything with that half then, hey, you knew this was hotly disputed.
But in the name of peace, you should just leave it alone. Or give it to your neighbor. Otherwise that is selfish.
They were being selfish by settling in that area to begin with, and cried foul when the Cardassians attacked.
"Selfish" implies a motive (and an improper one). "Hey, you staying here could start a war. And it could get you killed. And we have another planet just like it over here."
"No. We're staying just because. And we'll fight, steal, and kill for it. Because that's how we roll."
There has to be more to it than that. Maybe it's just that the settlement has a long tradition of existence. But it's not like generations of people grew up there.
The Cardassians shouldn't have been attacking worlds in Federation space, but those colonists didn't have to settle there.
I don't even know what to do with this one. "What can we say? You wandered into a bad neighborhood. Totally your fault. Not the fault of the people who robbed you and killed your family. They're just being who they are and you knew that in advance. Do something about it? Oh, heavens no. That could be bad and clearly you don't have a grasp of the situation. Let YOU do something about it? Are you insane?"
Those border wars might not have gotten so bad if they were empty planets... a negotiated peace would have likely been easier to make if those worlds were not settled to begin with.
Um... Sure? Same for the Cardassian worlds? "Here, Cardassia Prime. You can have these. They're yours. But don't use them or put people on them. Just be satisfied in the peace and knowing that they are yours."