Yes, you are right about research funding. I should have been more explicit, this is what I was referring to when I mentioned "business connections."
Private universities still receive some federal funding, which is one of the reasons that Trump's actions regarding sports being separated by biological sex has any impact at all. He can only enforce the federal funding side of things. So private universities are not entirely separate from public funds and the conditions that federal government put on those funds.
I think the reliance on alumni donations shows that it's riskier for a university to allow hecklers to stop debate than to say "no". As you say, " institutions will do anything to avoid losing those funds" and in my examples of Yale and Stanford, they're doing that by emphasising the importance of free speech and robust debate, not by allowing hecklers to veto ideas that they disagree with.
I'm a bit confused here, but I think we are agreeing/saying the same thing here? Sorry, am very tired this afternoon!
Re tuition fees: yes, US tuition, especially for private institutions, but even many state schools, is much, much higher than tuition fees in the UK.
I think, for two reasons, any university would weigh up their options here. If the "hecklers" are a minority of students, it wouldn't be worth the university pandering to them, to the detriment of the majority of students. Also, I think most universities are concerned more with optics than how much they might lose if 25% of those (minority) hecklers transferred to another university, taking their money with them. Demonstrations and such are par for the course at universities, but the university cannot let any kind of demonstration attract too much of the wrong kind of publicity. Protests against racism or apartheid in South Africa, for example when I was at university, were tolerated as long as it didn't spill over into criminal damage or rioting. Rallies lauding Neo-Nazis would not have been tolerated, but neither would protests preventing speakers (of any political persuasion) invited to the institution from speaking. Scary optics in national media deter prospective students and their parents.
I'm not sure that explains things very well!