Net neutrality is the principle that internet service providers should enable access to all content and applications without regard for the source, and without favoring or blocking particular products and websites. It is an important concept for innovation on the internet, and needs to be defended by the government.
A lack of net neutrality enforcement would mean that internet service providers could provide preferential treatment to their own services or to those that pay a premium, and that they could throttle or deny traffic to the others, allowing them to pick and choose winners among internet-based companies. We saw this in January 2014 when Netflix was throttled by Comcast – once Netflix negotiated a deal, their speeds over Comcast’s network went back up overnight. This was what happened before Title II protections were in place, and is something that could happen again if they are repealed.
There is a conflict of interest when service providers are also content providers, and a lack of real competition when customers do not have a choice between similar grades of service due to the high cost of installing redundant infrastructure (leading to regional monopolies). According to the most recent Internet Access Services report, published by the FCC April 2017, only 42% of developed census blocks have at least 2 providers that offer greater than 25 Mbps downstream and 3 Mbps upstream. More than half of those residential areas do not have a choice in broadband provider, if they even have access to broadband service (>25Mbps down) at all! This does not promote competition. Furthermore, the internet is an increasingly necessary part of our lives – ignoring entertainment and recreational uses, many jobs require internet access, and virtually all of them require applications to be filled out online. Consumers need protection from the monopolistic tendencies of internet service providers, in the same way that they do from power companies, water/waste, and phone companies – other utilities.
Before Title II was enacted, the FCC attempted to lay down these protections via the FCC Open Internet Order 2010. It was ruled in court (Verizon Communications Inc. v. FCC(2014)) that under Title I, the FCC did not have the authority to regulate broadband providers like common carriers. A return to Title I classification would likewise be insufficient to protect Net Neutrality.
It’s not entirely true that the only way to provide these consumer protections is via Title II protection enforced by the FCC, but it is important that these protections remain in place at least until a suitable replacement goes into effect; as an analogy, you shouldn’t repeal the traffic laws because you don't like the speed limit somewhere.