Tethering on unlimited plans is partly why AT&T got hit so hard when iphone users started signing up in droves. Don't get me wrong, AT&T's lack of infrastructure investment was surely the main part, but TBH, it's the people that abuse tethering privileges by canceling their home service and streaming absolutely *everything* through the cell network that ruins it for everyone else. If you didn't have so many people abusing the system, you'd see carriers using it as a value-add to get you to buy their unlimited data plan.
I hear over and over about people with their new unlimited VZ LTE plans canceling home service because *it's just as fast*. Well, believe it or not, wireless bandwidth is a much more limited resource than you think. The more tards that "cut the cord", the slower everyone else's service will be. Did you really think you were the only one smart enough to figure that out, D-bag?
I'd personally love the ability to tether any time for free, I'd root my phone for it. However, I'd also gladly trade that capability even with a rooted phone so that when I do USE MY PHONE for data, it actually works.