There are various interests in play, but what prompted the movement was the idea that ISPs were going to start billing websites to provide unrestricted access t

There are various interests in play, but what prompted the movement was the idea that ISPs were going to start billing websites to provide unrestricted access to their customers and invert the web. That idea was nearly universally condemned online and the first few people who came up to name a movement contrary to that called it net neutrality and started trying to come up with principles to fit what had horrified so many people. So the basic idea behind it is that ISPs shouldn't be able to indirectly charge content providers by threatening to block or restrict their content when it's requested by the ISPs customers. In other words, ISPs have no legitimate business meddling with other peoples' businesses, but different people have different ideas about what it is or isn't now.