Of course there are ways for ISPs to make more money. Caching FB content, guaranteed service for Netflix, or whatever...all that stuff does is make the ISP money. It's not doing me any favors. As it stands, I have no problems with my connection to FB, Netflix, or anywhere else. And my ISP has no problem paying their rent. Now, once they can start monetizing my QoS...it all goes out the window.
Like I said, contrary to your claim, the economics haven't changed. My internets are moving through the tubes just the same, and that's not going to change significantly in the future. ISPs' reward for upgrading their networks is that they don't get run over by the competition. There is no true gain to be had for users from any of this. If Cox cuts a deal with Facebook so that they get preferred service, I'm not going to see a discount on my bill. Know what I will see? A slow-down when I visit Myspace, or whatever other website that didn't pay the protection racket.
And to answer your question about why shouldn't ISPs be free to monetize their products however they'd like? Because they're monopolies. In many instances in America, government protected monopolies at that.
Not to get all ad hominem, but your OP falls flat. (My unqualified analysis? You get off on being contrarian for its own sake.) ISPs being free to do as you'd like will benefit nobody but the ISPs...and of course the Facebooks of the world who would have it that much easier to keep new competition at bay.