The fact that TMo gets to choose what data does and does not count against your cap should be an issue to everyone.
Why exactly?
This would be an issue if you couldn't turn it off. Or if T-Mobile charged a fee to those companies to add them to the list. Neither of these apply, and frankly i feel that lot of people complaining about this issue don't have T-mobile and don't have this enabled. Most of my data usage comes from watching Netflix, and Binge On is great. I get to drop to a cheaper plan because I'm not using as much data, and the DVD quality is more than enough for me on a 6S Plus.
I also don't see how this is a Net Neutrality issue.....T-Mobile is treating all data the same, the user is the one that decides that they want the data treated differently through consent (enabling or disabling Binge-On)....all T-Mobile is doing is facilitating the ability of it happening. At most the FCC may force T-Mobile to turn Binge-On off by default but i don't see it going anywhere.