You have to wonder if some of those colonists put themselves in that situation in the first place.
Establishing colonies right on the border of Cardassian space- where territory is hotly disputed.
It wasn't just the colony in Journey's End, but obviously other colonies as well. They must have been warned too.
If they were made aware of the situation and went ahead anyway, then I don't know.
They had the right to defend themselves, but I'm a big believer in looking before you leap.
The Federation is said to have plenty of planets for inhabiting and as stated before, all needs and wants have been easily taken care of already.
What's with the need for extreme risk taking like this?
Given some of the Maquis on Voyager cited being born on those colonies, it's perfectly reasonable to say they were settled before the first Cardassian/Federation war. They would have to be, being the Setlik III attack was the first aggressive act by the Cardassians.