You don't get it. The companies that laid all that fiber optic cable did so in most cases by being granted a monopoly by the government. You see, the government can't have 100 different companies laying network cable under the same streets. There simply isn't enough physical space for it, and nobody wants to sit through never-ending road construction because every time some company needs to lay down or repair or upgrade network cables the street needs to be torn up.
So the government awards the contract to one single company, to avoid the above problems. But then other companies, like Comcast, decided to buy up all these other local companies that had laid cable. And now Comcast is huge, and they don't want to be just a company that rents out use of their cables, they want to vertically integrate. And they want to use their monopoly over the cables to drive their competition out of business, and charge people more money for less service.
This is why we need net neutrality. f you are really a free-market capitalist, you will be in favor of net neutrality. If you want government-granted monopolies to be able to use their monopoly power to stifle competition by pricing them out of whatever business said company decides to enter next, then killing net neutrality is the choice for you.