That's absolutely worth a serious debate, but that endowment falls well within existing laws for how universities are allowed to accumulate and govern their finances.
You know what doesn't fall within the rubric of existing laws (or things that anyone who respect the rule of law and controlled government should be comfortable with)? Trump unilaterally using the federal agencies under his control to vengefully, punitively attack a major public institution just because he wants it to do whatever his latest personal tantrum has dictated.
His whimsical funding cuts are indeed illegal (1) and even if you agree with the government not funding certain institutions in certain ways, i'd call it a bad fucking idea to claim that the president should break his government's own federal laws to do so.
1 https://www.thefire.org/news/faq-responding-common-questions...