it's not their 'tollbooth', it's their road
It can be "their road" when they pay land owners for the lines through their property, and pay back the tax money that was given to them to subsidize its construction.
An eighteen wheeler can cause more damage to the road that requires more maintenance than a motorcycle, this is the same thing: a movie that needs to be streamed a million times takes up much more capacity and energy and basically uses the system much more than millions of small individual requests do.
Netflix is already paying a provider for bandwidth. You may or may not know this, Slashdot Libertarian, but as your bandwidth usage goes up, your bandwidth prices go up too. As such, Netflix is already paying extra money to run that 18 wheeler due to the wear and tear on that road. AT&T is trying to bill them extra because the truck is carrying a product that competes with them.
Is that their prerogative? No. They built their network on public dollars and on peoples' private property under the conditions that they would act as a utility. If they want to not act like a public utility, then they can come to me and pay me a fair price to run lines through my property (or better yet, since I don't use AT&T at all, how about I just cut their line? It's my property after all.)