In an economic context, why would it not be fair to judge the economic worth of someone’s degree on the basis of that degree’s ability to influence their earnings?

Because there are a litany of counterexamples to the myth that earnings equate to economic value. Teachers, police officers, and social workers immediately come to mind.

That sounds like a great argument for subsidizing teacher and social worker education instead of the wholesale forgiveness of student debt which includes people with degrees in poetry and pottery. Poetry and pottery are both valuable to society, but honestly a lot of the people who are good at those things don’t have matching degrees. Also, forgiving loans for pottery degrees competes with our ability to subsidize education for teachers.

The obvious solution is to subsidize teacher pay etc, not to subsidize education to be teacher! If teachers are well paid, you wouldn't need to subsidize teacher education.

Subsidizing teacher pay is subsidizing education.

Yes but having an educated citizenry pays dividends in a multitude of non-economic contexts.

Unfortunately, degree != educated.

For most intents and purposes, pursuing a degree entails attempts to become educated.

Some works of art may have value beyond their auction price, but you probably shouldn't buy them if you can't afford them.

If I'm expected to pay for it with tax dollars, that's the only possible way to view it. I'm not going to subsidize someone "finding themselves".

No, you subsidize people doing poorly paid but highly educated work in fields like public health work, education, and non-profits. You also subsidize people getting the basic education required for many jobs.

Many jobs do not require the "basic education" that a college degree provides - a HS education is entirely sufficient, and was widely regarded as such even as late as a few decades ago. It's a wasteful credential-chasing arms race, and the more we keep subsidizing it the worse it will get for everyone involved.

Much like welfare and food subsidies in my view its morally unacceptable when you start judging an individual's worthiness rather than their need.