Such could have been said about the krogan or quarians as well, but look what heights they may rise to again.
It's entirely possible that Orlais will be in no shape to oppose them, and that assumes that the Dales will even be the place they retake. In any case, the elves owe humanity nothing.
And how are the elves going to be in a possession to oppose orlais? or ferelden? or Antiva? or Nevarra? if the elves were to take the Dales, and then try to take lands from humans, another exalted march would be called immediately.
And this is assuming they don't call a march immediately once they all arrive in the land. If they take it with violence no human nation will ever let them keep it.
Especially if they lose workers to the Dales, the peasants would hate every elf since its their fault the economy was damaged.
And this is all assuming the Dalish were able to come from every corner of thedas in a timely manner, cross through orlais, and then somehow establish places for the elves already living there, and for them to live. And thats not talking about the hate which would spawn between the Elves from the Dales and the Dalish.
Also the dalish barely have a population anymore. you even hear that they wouldn't accept elves from the city but their numbers are so low they have to.
Society changes, we know some humans in the cities want lives for the elves to get better. so right there we see a abolitionist movement.