If Americans could choose between spending $1.5 trillion on eliminating student debt or giving a 10 year tax cut in the same amount to corporations and the top 1%, which way do you think we would go? Which way do you think we should go?”
You may believe you are advocating for a "cause" that appears to be beneficial to the public purpose, but you are framing it in the language of fiscal scarcity that serves to kill all such legislation. What if the correct answer is to do both? Is the public purpose served by both? If so, then that is what Congress should do. There is a strong argument for not collecting federal tax from productive businesses and the benefit of free public education is a no-brainer.
The US dollar doesn't grow on rich people or their corporations. It is a product of law and codified in Article 1: Section 8, giving Congress authority to create currency as needed "for the general welfare". Full stop. No "revenue" is necessary as taxation doesn't really "fund" anything at the federal level. The US dollar is self-funding when it is spent into existence in the private sector and is destroyed when it is collected as a federal tax and applied against the debt that created it.
It would be one thing if the U.S. were short on money for everything, and in the process of making hard choices for all of our national spending, we decided that we had to take hard lines on all non-essential spending choices.
The US Congress may find itself short on necessary resources, such as teachers and facilities, but it cannot ever be short of the money needed to deploy those resources if they exist. As the monopoly issuer of a sovereign fiat currency, Congress can "afford" anything that exists, or potentially exists, and is priced in US dollars it creates at will.
If the hard and soft infrastructure to supply Americans with a desired level of education at no charge doesn't exist, Congress should spend whatever it takes to supply them and spend on the students themselves, including living expenses as many other countries already do.
None of this should be contingent upon "revenue". At the federal level, the US government neither has nor doesn't have "money" and conflating the currency issuer with one's household budget experience with dollars only lends itself to the protection of the status quo.
I guarantee that your desire to see universal higher education is already unnecessarily being fought on two fronts, the merits of the issue itself, and the "funding" of anything via taxation. If you think that education funding should come from corporations then you must commit to perpetually assuring those corporations remain profitable enough to supply that funding.
There is far more power in making a person or entity irrelevant to your purpose.