So like others my first reaction is that of COURSE unlimited means unlimited and that they shouldn't throttle after a certain amount. I have Verizon unlimited and enjoy that's it's truly unlimited and I can use it as a hotspot too. AT&T's perspective is generally that they are giving you an unlimited amount of data but controlling how fast you can actually use it.
Let me ask a similar question.
If I go into a restaurant that heavily advertises unlimited breadsticks, can I reasonably expect UNLIMITED breadsticks? Or is it reasonable for the restaurant to say sure, it's unlimited, but we'll only bring out 1 per person at the table at a time?
I think we'd mostly agree that the latter is acceptable and that a request for 1000 breadsticks would be declined. Is that really any different than what the carriers face, where 95% of customers use 2GB or less and probably 5% are far more than the other 95% combined?
Certainly bandwidth is less of a tangible quantity than a breadstick -- it's harder to argue that I am being wasteful by using 100GB. But, let's not act like bandwidth is an unlimited resource, either. It does cost money to expand capacity and if the bulk of that is being forced by a few users sucking down enormous amounts of data then they are indeed a very real cost to the carriers and to all of us.
Dunno what the right answer is, but I do think it's far more complex than the FTC's argument that unlimited means unlimited.