Oh man, this is so in my wheelhouse. You are so very wrong. Here are bunch of reasons why:

First off your definition is wrong. Net neutrality, simply, is the idea that your ISP has to treat all data it sends you the same. The repercussions of this are not just throttling and not throttling, but potentially not even delivering packets.

Reason 1: Protection of the free market

The consumer is in no way equipped to know when an ISP is throttling data, or simply not delivering it. Net neutrality is not an easy concept to understand. Noticing it in action and understanding who is responsible for doing it is orders of magnitude more difficult. Even in the Comcast/Netflix case, there is no way for even a tech savvy consumer to know if the slowdowns were coming from Netflix targeting Comcast users, or vice versa.

This means that there is no way for a consumer to make an educated choice when sites are blocked/unblocked or sped up and slowed down on the fly. It's not competition if the user is unable to know what they're paying for and when, and strict regulation on disclosure of network speeds would be even more invasive than blanket net neutrality legislation.

Reason 2: It would quite literally break the internet

The government created the internet. It's their baby. If throttling were to become common place, small websites with large bandwidth consumption that were seen as competitors would be pushed out immediately. It would make trying to catch anti-trust violations a damn nightmare. And again, consumers would have no way of knowing what's happening.

Reason 3: Isolation through information spheres

This is the most alarmist view of net neutrality, and one I haven't heard anyone other than me comment on, but it seems like it would clearly follow. Today, if companies like Comcast and AT&T are allowed to silently shut down Netflix, without their customers knowing what's going on, that's bad. But it's not catastrophic. What gets catastrophic is a decade down the line. Slowing and editing packets is now commonplace. There are no non-sanction competitors, but now look, AT&T and Comcast want to merge! And then, the CEOs of companies learn that it's really a simple matter for the guys in IT to just remove all articles that speak badly of the merger from the sites of their customers. That would make perfect business sense! You control such a huge chunk of the market, why allow your customers to participate in something that's detrimental to your bottom line? And this technology already is so advanced that customers would never even know it. That NYT article about AT&T and Comcast? Won't load. Those Google results that talk about the downsides? Don't even appear.

What are consumers going to do? It would be incredibly hard to discover, and harder still to prove. Especially when your only source of information is your data provider.

This could clearly evolve to corporations allying themselves with political candidates. They think the republicans will be less heavy handed with regulation, so they remove positive articles about the democrats. Or vice versa. Maybe consumers find out at some point, but it would be slow and gradual. Eventually we would just have spheres. Your ISP exposes you to the internet they want you to see. End of story.

TL;DR The internet is the most important invention since the movable type printing press. It has to be protected or there will be dire consequences to our liberty both politically and as consumers.