Two things:
(1) Net neutrality is mainly a fight between infrastructure owners and Internet content producers; Comcast, Time Warner, etc., want in on the giga-bucks made by content providers like Google and Facebook. Right now Infrastructure owners own and maintain expensive networks. If they could 'tax' content providers for using their networks, infrastructure providers would have an additional stream of income and could lower prices for consumers in competitive markets.
But this 'tax' would be passed onto consumers. $7.99/ month streaming Netflix could become $12.99/month streaming Netflix. Google and Facebook wouldn't be as profitable, or at least would have less money to throw around on new projects. Post-merger Comcast/NBC could slow down ABC and CBS streaming videos in favor of NBC. Hulu would become more expensive. YouTube may have to rethink its business model.
(2) The legal debate is whether Congress has passed a law authorizing the FCC to make such pronouncements about infrastructure. The FCC passed on regulating cable TV and physical phone lines a long time ago (although there are still legacy telephone issues it can regulate). IIRC, the FCC is the most likely to be able to mandate cell phone and wireless net neutrality, because regulating traffic on the airwaves has been one of its powers since 1934.
It may be that the FCC can regulate 'land line' Internet in some fashion. In the early 2000's, the FCC decided that the cable modems (and likely DSL modems) provide information services, a class of service over which it does not have much regulatory power under the 1996 Communications Act. Under that Act, however, the FCC does have power over telecommunications services, and it will likely (or maybe it already has?) reclassify 'land lines' as such. Regulatory agencies are generally allowed to change their minds about such things (provided it's justifiable).
A note to lawyer-mans and fellow travelers; the foregoing is a gross oversimplification of regulatory law because this is a goddamned video game forum. I'd be happy to argue about whether the FCC has no choice but to label 'land lines' under Chevron, but I think most folks are bored out of their minds by arcane discussions of admin law.