Considering most (wired) broadband is bandwidth-limited at this point, varying that bandwidth limit based on what site I'm talking with just feels wrong, and I'd love to see the practice banned, because as you mention, a lot of users have no choice in what broadband they can subscribe to.
Wireless broadband is almost all capped in the quantity that you can use, however, and the T-Mobile "free streaming" options mentioned give you something extra for "free." This is in stark contrast to blocking/limiting something you're paying for, and I would be fine with this limited exception in the wireless space.
But what I would like to see, since this is effectively a utility, is for that "free streaming" to be available on an equal opportunity basis: And T-Mobile seems to be doing exactly that by allowing customers to vote on what services to include.
What feels like unfair competition is (as you mention) Comcast shaking down its competition by way of not providing customers equal access. And until that last-mile competition problem has been otherwise resolved (Google Fiber everywhere?), I think we do need those regulations to prevent monopolistic behaviors.