It's not fair to high school students who sacrificed hours that could've been spent working or on fun to do dual enrolment classes at a local college or take AP classes (and paid to take AP tests) so that they could save money on a semester or two.
It's not fair to people who worked hard as teenagers to acquire scholarships so they wouldn't have to take out loans. And it's not fair to people who in college worked hard to obtain or maintain scholarships.
It's not fair to people who spent time planning where they'd go because they were trying to go somewhere affordable. That includes people who did community college, people who chose online schools, people who did part-time schooling, people who chose a school close to where they live, and people who chose to go to affordable colleges.
And of course, it's still not fair to those who didn't go to college. I think of my brother who decided to skip college because of his entrepreneurial work ethic. One of his ventures failed during the 2008 crash that made it so he had to move back in with family with his wife and kids. Loan forgiveness means he's stuck footing the bill for his friends who work in fields they didn't get degrees in and spent their loans on lavish summer trips abroad to "find themselves."
The cost of student loan forgiveness is not just the amount that we as taxpayers will owe in order to benefit the most fortunate in society. It will have long-lasting effects because it will incentivize unproductive and bad behaviors or disincentivize productive ones, which slows down progress and limits prosperity.
Student loan forgiveness is perhaps the only policy that incentivizes bad consumer behavior en masse and benefits the "rich" at the expense of the "poor."