Re: Why "net neutrality?" Simples.
1. It is not the job of any corporation to evaluate and act for the public good. It is their job to make the largest possible profit for owners and shareholders.
Obvious corollary: corporations will always act against the public good when there is profit in doing so.
Historically, this is accurate. Phillip Morris' decades-long attempts to keep customers from knowing that cigs are really cancer sticks is an obvious example. Ditto Ethyl Corporation's decades-long attempts to hide the neurotoxic effects of the lead exhausted from tetra-ethyl anti-knock gasoline. Corporations running phone services made money selling customers private information without customer approval or knowledge. Congress told them, "That's wrong and bad, stop doing it." The corporations agreed to stop. But they did not stop selling private info, because it makes more profit for them. And so on.
2. It is, in the US, the job of the government to safeguard the public good. (All citizens have rights, and "Governments are instituted among men ... to safeguard these rights".)
Logical conclusion: since it is known that corporations will violate the public good in order to profit, and since it is the job of governments to safeguard that same public good, then it is prudent for governments to make rules proactively to forestall erosion of the public good -- say, by selectively throttling customer's internet access based on payments from content providers.