No, we should not "cancel" student loan debt
The proposal to "cancel" student loan debt is one of the more openly socialist schemes the Democrats have proposed, and is a bad policy on both economic and moral grounds. It is also an obvious political move to solidify support among Millennials for the eventual Democratic nominee. Promising to take money from some people to give to your supporters is a cynical move.
I can understand a limited program that would provide relief on a case-by-case basis to people who are truly in need and are being financially crushed by student loan debt. For example, people who could have paid their loans back but became ill or were seriously inured, racking up even more debt. Allowing people to take huge "loans" and not pay them back, however, just encourages irresponsible behavior. Subsidizing irresponsible behavior will increase that behavior.
Furthermore, federal policy has increased the cost of college by insulating consumers from the cost of the product. Student loans and grants have allowed people to not feel the cost of college until years later, but if people were more directly aware of the cost while in college they might be more discerning in how they incur debt or where they go to college. "Forgiving" student loans would make that problem worse, not better. It will also cause a dramatic increase in the cost of college by further insulating it from the market forces that would otherwise work to push down the cost.
Given that people with college degrees are generally better off financially than those who did not attend college, this would be a welfare program for upper-income people - something that Democrats have traditionally opposed. I guess principles vanish when an important Democratic constituency stands to benefit.
Finally, this is not a program that should be handled by the federal government. If the states want to provide relief to their own citizens, it would still be a bad idea but would be within their authority to do so. The federal government has no authority under the U.S. Constitution to "cancel" well over a trillion dollars in student loan debt. I realize that the Tenth Amendment has been ignored for generations, but this does not mean we should continue to push past constitutional limits on federal power.