“If the end of Net Neutrality is the end of the world, how in the world did we exist on the Internet before they were put in place?”
There were two phases. During the 90s, line-sharing requirements created a competitive ISP market, and market forces prevented widespread abuse. Then under the Bush administration, those requirements were killed, and overnight we wound up with local monopolies (or for the lucky minority, duopolies). Within a few years there were numerous reports of abuses — not just poorly thought out prioritization schemes, but interference and tampering with Internet traffic. One of the most prominent was Comcasts’ interference with BitTorrent, something people are still wary of even a decade later.
In response, the FCC attempted to regulate the local monopolies with Title I net neutrality requirements. Verizon sued and the courts found that net neutrality requirements could only be imposed by a Title II classification, which was implemented in 2015, and ever since we have enjoyed a neutral wireline Internet (the mobile Internet is not at all neutral, but there we have a competitive market that is slowly correcting the abuses of dominant players).
Also keep in mind that the issue here is not just about throttling one website or paid prioritization of another website. A neutral Internet supports applications in general, including applications that do not have a clean division between “consumers” and “providers” — i.e. peer-to-peer applications like BitTorrent, Bitcoin, etc. If ISPs build a network that is designed to support specific kinds of applications, e.g. if fast lanes are created for certain websites, we will be locked in to a system that does not support new uses for the Internet itself.
In fact we can observe that very effect already. Cable companies provide Internet service that is designed to support only applications where large amounts of data are sent to residential users, with far less data being sent from residential users (asymmetric speeds). The DOCSIS standard is set up for this use-case and makes it technically difficult to provide symmetric speeds. Cable companies are locked into that architecture, to the detriment of customers who use applications requiring symmetric speeds (non-exhaustive list: online video games; peer-to-peer systems; video conferencing; etc.).
Remember, the Web replaced the systems that preceded it; something else will eventually replace the Web. If the US allows ISPs to build systems that hamper next generation applications, we will wind up in second place, behind countries with neutral networks whose citizens can immediately benefit from new applications without waiting around for their ISPs to make deals (assuming there is even a deal to be made i.e. assuming the Web is not replaced by a peer-to-peer system).