"Good" is a subjective term. To do some good for some, you have to do bad to others.
Some people want to give the elves the Dales. This, in theory, it's good. Elves suffer much in human cities.
But it can lead to much "bad". First, there are many humans in the Dales, some are civillians living there, others are soldiers fighting in the civil war. All of them would have to be forcibly ejected regardless of their moral character, which is bad.
Then, it remains to be seen if the elves could mantain a state. We could be looking at cultural conflict between the Dalish and the City Elves, each with different notions of which direction the state should go. In fact, it could get even worse than that, there could be conflict between elves from different nations. I doubt Orlesian and Ferelden elves have any love lost for each other.
And what about conquest? The Dales would be the weakest nation in Thedas and the Chantry would accuse it of being composed of heretics who slaugthered and ejected the faithful. We could be looking at Exalted Marches or simple conquest. An attempt to do good could lead to much bad.
And that is assuming they suceed. The elves in Halamshiral rebelled but little good that did them when the Orlesian army arrived and burned the section of the city the rebel occupied in a couple of hours. If the elves try to do this and fail, their condition will just worse.
Who says giving the elves the Dales necessitates displacing the people who already live there?
For one thing, between the civil war and the Breach, many of those soldiers will not be coming home.
Not to mention the Exalted Plains (just one area within the Dales proper) is described as "a massive stretch of land".
As for potential conflict between the Dalish and the city elves, look at Rivain. If elves, humans, Andrastians and Qunari can coexist peacefully, certainly elves can.
The Chantry is in no position to call an Exalted March. They no longer possess a martial arm. Their military strength is gone- the Templars, seekers, and Circle mages are preoccupied. Orlais is rife with civil war. The major players will be looking for support. What better time for the elves to parley?