An absence of net neutrali9ty means that internet providers could effectively censor the web of material that offends the political, economic, or cultural interests of the provider. Comcast might block one from getting any programming schedule for networks competing with NBC.
Internet providers could make special arrangements that essentially block alternatives, thus supporting monopoly in marketing. They could censor something like Project Gutenberg so that Karl Marx would be off limits so that one could never contemplate him as an answer to a bad capitalist order, or Bertrand Russell for his atheism. (Even if I were a Christian supporting libertarian capitalism, I would want people to know about Marx and Russell so that people could discuss what is wrong with them). Thinking of a uniion to improve conditions at work? Perish the thought -- by killing access to any pro-union material.
Is there any evidence media companies were actually doing that, though? There's never been any difficulty finding left wing subversive content on the web and the big companies could have been doing this all along if they wanted to.
The only thing net "neutrality" does is enable the government/FCC to do things like that since they're the ones who define what constitutes "neutrality" with no possibility for judicial review if I recall correctly. So if you don't think the way the FCC is administering this stuff is neutral you can't sue them. With
Trump of all people in charge of the executive branch you'd think that would be the last thing the left would want.
