But, even if we were to take your assumptions at face value, I'm not sure how you gloss over other details (such as their ability to price competitors like Netflix out of the market or essentially hold their users for ransom to the highest bidder).
Given that they are quasi-monopolies in most cases, these are certainly issues that deal with consumer choice on one end and access to opportunity on the other (i.e. for content providers, startups, etc.). In other words, these are issues of fairness. How can something be both made willfully unfair, yet be ethical? Would you not agree that fairness as a principle is morally right? That is the definition of ethical.
You made the argument in another comment that it's no more a matter of ethics than is raising taxes. But, certainly you can envision a scenario under which taxes can be raised in a manner and/or at the behest of certain groups which would make it unethical?
If none of this makes sense to you, then therein lies the divergence. It's one regarding the basic definition of ethical.