What's the deal with Net Neutrality?

I've always felt that it's a bit vague and more fear-mongering than is necessary. So what is really going on here?

I understand that the topic is related to governmental or federal regulation of [mostly] practices of Internet Service Providers. Shit that Verizon pulled in the recent past rings various kinds of alarm and seems to warrant a lease on its neck.

Oh, let's not forget about this image either:

 Spoiler

This alone seems enough to make Net Neutrality look appealing. Still, what does it mean to enforce these new rules? This Forbes article (agenda notwithstanding) gives some insight.

From the outset, however, the FCC’s effort to pass any net neutrality rules has run into two very large problems, one legal and one technical. The legal problem, the one the D.C. Circuit will eventually address, is that Congress never authorized the FCC to regulate broadband Internet services.
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The technical problem is more worrisome still. As commercial uses began to appear in the mid-1990’s for the once research-oriented Internet, engineers have innovated in a wide variety of ways to optimize performance of the rapidly-expanding network. The Internet, even at the engineering level, is not “neutral” in the way it routes packets and perhaps never was.
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So, what is this guy saying, and how could these be reasons to vote against Net Neutrality instead of problems we'd just have to try and come up with solutions for? It seems (as I can dig out from his highly difficult manner of writing) that it has to do with this one particular complaint/objection:

What’s so dangerous about that? The short answer is that innovation delayed is innovation destroyed. Consider that the FCC spent over a year just to develop its Open Internet report and order, during which time more essential work of the agency languished. Verizon filed its legal challenge as soon as the rules went into effect. It has now taken the court another two years to take up the matter, and an unknown period before they actually reach a decision (which may require further proceedings).

None of these facts is unusual or even objectionable. Regulatory agencies are designed to move slowly and deliberately, and courts are designed to operate even more carefully.
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That freedom is what is at stake, ultimately, in Verizon’s challenge of the FCC’s Open Internet order. The freedom of users to access the legal content they want is not at risk. But the freedom of network engineers to continue innovating, without the micromanagement of poltically-appointed regulators. is.

Stifled innovation caused by slow over-regulation. Sounds reasonable enough on paper. Disappointing if this is the best that anti-NN can come up with.

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So that's my (mis)understanding of the situation. Question time.

• What are the actual motivations for NN? Who are behind it? What do they gain with NN? What do general users gain with NN?
• Aside from Verizon and other telecom monopoly wannabes, who are against it? What reasons/objections do they propose? What can we lose if NN goes into effect?
• Can monopoly not be dealt with by existing anti-trust laws?
• Considering the frightening resemblance between the state of cable TV and Verizon's recent bullpomegranate, how worried should I be?
• What questions am I being too dumb to ask?