Why is net neutrality important?

This my own personal take on net neutrality. Let me know your thoughts on it.

The essence of net neutrality seems to be that the consumers (and not the ISPs) decide what websites to access. There is one internet and no matter who your ISP is, you access whatever apps and websites you want to access without any sort of prioritisation.

That being said, I think net neutrality questions the whole idea of a competitive market. The Internet companies did the hard work to build their infrastructure and I believe, they can choose to cut a deal with a particular company like Facebook and prioritise it over say Google. Facebook would load faster than Google on say Verizon, as compared to AT&T. Why is this wrong? It's pure business.

Edit: My own personal musing. Just to get a better understanding of the whole net neutrality argument.