The US first amendment protects all speech, not just political speech. Most particularly it protects offensive speech because that is the only kind that needs protecting. We endure many inefficiencies for the freedoms we allow, the idea is that those freedoms are worth the cost.
Indeed, if the drafters had forseen corporatism many things might have been different. And then there is the organized persecution of peers for their horribly offensive (read differing) opinions that is allowed by our modern communication tools. Is freedom of speech freedom to persecute? Maybe having really bad ideas should become a protected class? I say that only half jokingly, I have no answers.
The drafters didn't foresee protected classes (in the legal sense you're using the term, if I understand correctly); in fact, several of those protected classes simply weren't granted the rights granted to white male landowners by the Constitution the drafters framed.
I don't know how much guidance we can take from the original drafters on the novel problems of the modern era.
At what point do we stop calling a company a small profit-taking endeavor and start calling them a government in everything but name? When they have a monopoly over national communication infrastructure? When they control a small city complete with infrastructure just to service a Florida theme park? How about when they overthrow foreign governments to grow bananas easier?
Well some companies are starting to look more and more like the government. Besides corporations are protected by the government from certain things. The populace should be protected from their actions as well. Existence of big corporation always affects life of many people so it is only fair that those corps should be restricted in what their can do.
For one thing those corps main duty is to make money. If they engage in morality setting instead they should have their business license revoked.
Battles can be fought on multiple fronts if necessary.
This isn't the first corruption coming from ICANN.