Misguided Rohirric policy towards Dunlendings?

[Tuor of Gondolin]

From "the complete guide to Middle-earth", by Robert Foster
"In the Third Age they hated the Rohirrim, who had driven them out of the northern valleys of the Ered Nimrais and the plains of western Rohan, and so they frequently attacked that country."
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Should/could Rohan have adopted a more "enlightened" policy towards the Dunlendings? It seems their policy towards other peoples (including the Woses) was more akin to the United States and Australia towards their native peoples, as opposed to that of Canada's or New Zealand's more generous policies. Given that the land between the rivers Isen and Adorn was very lightly populated, couldn't an accomadation, perhaps including the Druwaith Iaur [with agreement from Gondor] have been made for a sort of "autonomous Dunland" that would have been an ally, not an enemy. And why was such a generally "good" people so virtually paranoid toward people different from them (for example, Eorl still negative towards Elves after Galadriel helped him get to the Field of Celebrant, and the Rohirrim's treatment of the Woses?
Rohans treatment of the Dunlendings seems especially curious since it is stated that some of the Dunlendings were absorbed into the Gondor polity.

And yet the Rohirrim still come across (to myself included) as a "good" people. Perhaps an example of no one or no people being without flaws?