Comcast has shown through blocking Pirate Bay and extorting NetFlix that the potential for ISP's to abuse privileges provided by deregulation are much to high.
ISPs, by definition, are paid by customers to create and maintain connections between individuals, companies, and services available on the internet AS A WHOLE. The Tiered Service Model would not be strictly illegal under (true) Net Neutrality, so long as the terms of service for whatever bandwidth usage is agreed upon by the contracted customer. It is detrimental to the internet to deny or slow access to or from any entity, and is unethical (and should be illegal) to block or slow competitors sites while favoring the ISPs and its partners. The internet is an infrastructure & utility, not a commodity.