How could it be a good thing, that Hassan and Ali are forced to move to Hajarajat?

This region was at least home to the Hazara ethnic group. They might have had a chance to survive the terrible prejudice in other parts of Afghanistan.

They won't be persecuted where they live and can start a fresh new life. Like Hassan became literate. If he hadn't moved there, he would be illiterate. It's also a sanctuary. He didn't feel categorized in a class.