You're only looking at the end user side of the ISP market
Net neutrality addresses the edge provider side of the market--it's a debate over whether ISPs can use their gatekeeper status between the edge provider and the consumer to extract more profits from the edge provider. In some instances--say for Facebook--it's beneficial for Facebook to pay the ISP for a fast lane so long as all other traffic is related to a slow lane, because tiny variances in load time actually equate to huge variances in traffic (250 milliseconds is the threshold, according to Microsoft). So, by paying to be in a fast lane, Facebook is creating a barrier to market entry for all future competitors, and VCs won't even bother investing in potential competitors.
In short: net neutrality is about whether ISPs can flex their gatekeeper power over edge provider's access to consumers, artificially imposing bandwidth shortages in order to extract more profits and provide competitive advantages for those companies willing to pay for it.Allowing ISPs to do so happens to ruin everything that is great about the internet: open, innovative, competitive, quirky, varied -- that internet is now dying.