[Caveat: I don't know if this is exactly accurate, so if I'm slightly off, or if the analogy doesn't work, feel free to supplement/amend.]

Imagine data is like water: you pay a provider so that it can come into your home. Those providers have huge initial capital outlays to establish distribution networks, and often rely on power of eminent domain to overcome geographic barriers and be able to reach end users. Based on how much you use, you pay more. But there are some differences between water and data, which accounts for whether or not we should treat ISPs like utilities.

Everyone pretty much agrees that ISPs should be allowed to charge more for users who use more data (if they want). They should also be allowed to offer unlimited data, if they want. Water companies, on the other hand, have to charge by the unit--there is no other way for them to recoup the fixed costs of distributing water other than by volume. There's no "unlimited water" plan that I'm aware of.

Everyone pretty much agrees that ISPs should also be allowed to charge customers differing rates based upon the speeds, or rates, of your upload/download speed. If you want 100MB/sec, it should cost you more than if you have 10MB/sec, or less than if you want 5 gig/sec. This is different than water companies, who charge you the same if you fill up 10 gallons at a rate of 1 gallon per minute using a bathroom faucet, or at a rate of 5 gallons per minute using a hose.

Finally, after taking into account differential pricing for volume and rate, imagine that there was differential pricing based on how that water or data was used. For instance, if you filled up 10 gallons in a washing machine at a rate of 2 gallons/minute, it would cost you x, but if you filled up 10 gallons in a bathtub at a rate of 2 gallons/minute, it would cost you y. Then imagine that the water company is also in the bathtub manufacturing business, and could give you a discount if you fill up one of their bathtubs, but would charge you more if you used the same amount of water filling an off-brand bathtub at the same rate. That is perhaps the closest analogy to what net neutrality seeks to protect against: a dynamic where everything that uses water (bathtubs, washing machine, hoses, dishwashwers, sinks, sprinklers) is put at risk not because they make an inferior product, but because monopolistic pricing allows providers to undercut end-use products.

Honestly, there are some differences, and some similarities. And I'll say that there are legitimate pros and cons to both sides. Even still, and while acknowledging the ways in which ISPs shouldn't be treated exactly like regulated utilities, I think free markets are best served by supporting net neutrality: You still have elements of competition (service, plan levels, upload/download speeds) that ensure competitive markets among ISPs, while making sure that entities that rely on ISPs (content providers, websites, etc.) are also maximally competitive.