That's overly simplistic.
Kid A (and Kid B, both being taxpayers) are *also* paying federal taxes that go toward Medicare, Social Security, corporate subsidies and tax breaks, necessary military spending, wasteful military spending, some dud programs, some potentially worthy programs, and every other kind of government expenditure.
Debt forgiveness isn't some newfangled thing, it goes all the way back to the Code of Hammurabi.
https://slate.com/business/2022/08/student-loan-forgiveness-long-history-debt.html
It is a policy that, for once, places young people's interests front and center. That's why Biden's debt forgiveness carries 85% support among Americans under 35, regardless of whether or not they went to college.
Rampant inflation in higher education spending ought to be addressed in a systematic way, but this is a policy of necessary relief that can be implemented *now* while we wait for Congress to get off its ass and figure it out.
By the way, that's not to say we shouldn't *also* be forgiving other kinds of debt, like medical debt. The way our health care system shoves families into bankruptcy is shameful, and there's no reason we can't figure this out like other countries have (see chart).