There's nothing wrong with allowing cable companies the freedom to "segregate users" and create a caste system based on an ability to pay. That's essentially the same freedom mobile providers (Verizon, Sprint, etc.) enjoy with regard to pricing their respective plans. In a free market, that same freedom would be considered a given regardless of industry.
The problem with cable is that, like telecom, it's a regulated monopoly (a fact that music4mic already implied). The cable companies have been granted the right by municipal governments to be among the few select providers - and sometimes the only provider - in a given area. (Admittedly, that's an oversimplification. Here's an
old article that describes the process by which this happens. To say the process is convoluted is an understatement.)
Once a regulated monopoly has been established, the companies that have been granted the right to "serve" the community are essentially protected from competition. They can do pretty much anything they want as long as they avoid stimulating the ire of their regulatory masters (politicians). Customers have few options due to the monopoly created by their elected leaders.
Net neutrality seeks to obligate cable companies to provide equal access across the board. That's a very populist notion. Everyone hates their cable providers. They feel like they're getting screwed by them. So most folks support the idea of forcing the cable companies - i.e. the "bad guys" - to provide equal internet access at the cost of their profits.
But people were actually screwed a long time ago by their governments. That's how the cable providers came to enjoy their monopoly (i.e. protected) status in the first place. Asking those same governments to pass laws designed to force cable companies to provide equal access is dismissing the role that regulation played in creating the problem.
There are economic reasons to hate net neutrality laws. But those reasons are all but irrelevant given that so many folks have been bamboozled by simple chicanery on the part of their leaders.