What moral basis? I'm not sure. I just know at the age of 32 I am still in debt up to my eyeballs and went to a SUNY School. Most people I know in their 30s are renting because they can't afford a mortgage because they are paying $500 - $100 a month in loans. I think the economic benefits of forgiveness would far outweigh the negatives.
As to a mortgage, when your mortgage is paid off, the value of your home is (hopefully!) still worth at least the principal you paid and likely much more. It's an extremely valuable asset. So too, of course, is an education, but it is not a tangible good.