One side says that people who operate the internet must treat all data packets the same, whether they are from
youtube.com or
grandmascats.biz. The government will force the companies to treat all traffic the same, making the net "neutral".
The other side says the businesses that run the internet and traffic should be able to treat different traffic how they want, that the government should not interfere. If they want to give
youtube.com priority over
grandmascats.biz, they should be able to, as a private business. Which by the way, is how the internet has been running for the last 30+ years.
The pro net-neutrality people say that it will prevent companies in the future hamstringing traffic they don't like or of competitors.
Those against net-neutrality say the internet has been fine up to this point, as a thing the government has been hands-off on. And let's not have the government start getting involved in the internet, regulating it, and getting their foot in the door, even if it is supposedly for everybody's good, especially to fix something a future problem that doesn't even exist yet.