Let's say Comcast's bandwidth cap is equivalent to the property owner of a mall charging you for an hour's worth of shopping access. You could shop at any store you choose (net-neutrality) but once that time limit is up (250GB data cap), you're going to have to pay extra for more access.
Are either one of them entitled to charge you that way? Sure. Does it seem right? Not so much. But why not?
The property owner doesn't have to charge you access to the mall because they're getting rent from the stores. Unfortunately, Comcast isn't getting rent from websites. So it seems they should be able to charge users access to those sites however they please.
No one wants bandwidth caps, but there doesn't seem to be a compelling reason why Comcast can't do it, or shouldn't do it. Comcast owns the road and can certainly set up as many toll booths as they please.
And that saddens me.