The arguments in favor of keeping ISPs regulated under Title II are plentiful.
One of Pai's core arguments for reversing the act is that it has stifled competition among smaller ISPs. But some lawmakers, including Democratic House Minority Leader Nancy Pelosi, disagree and are in favor of keeping ISPs under Act II. "Consumers should be able to use the internet on the device they want, using the apps and services they want without their internet provider standing in the way," Pelosi said in June.
There are also fears that ISPs will throttle data and could potentially block access to services that they fear are in direct competition with their own offerings. Imagine, for example, if one provider blocked Netflix because it wants its customers to instead view its own suite of on-demand movies and TV shows.
The Verge's Nilay Patel thinks that reversing the act will make the internet landscape will look a lot more like mobile broadband. There, carriers are already doing all sorts of things that are not allowed if they're regulated under Title II.
For example, wireless carriers can throttle data to slower speeds if you use too much, charge you for different internet usage features (like using your phone as a hotspot), and tack on fees if you want to stream video in HD.
With the current act in place, ISPs can't do what we're seeing in mobile.
Title II also gives the FCC the ability to tell ISPs to stop doing something, like throttling data, while Title I does not. Ben Thompson from Stratechery references an instance in 2007 where Comcast throttled data on peer-to-peer content-sharing network BitTorrent. The FCC was not in a position to tell it to stop, since at the time Comcast was regulated under Title I. Comcast ultimately lifted the throttling anyway.