The rationale is that the broadband providers are creating "fast lanes" that will enable companies that are willing to pay extra (think netflix, amazon, and google, mostly) to get to consumers more easily.
Unfortunately, this rationale is horribly misleading, because they aren't creating new lanes. They're just repurposing some lanes for exclusive access to those who want to pay.
In the DC area, on the Virginia Beltway (I-495), there are now what are called HOT (High Occupancy/Toll) lanes. Basically, two lanes are reserved for those willing to pay to travel on those lanes. The idea is similar, but the difference is that they didn't take two lanes away from the existing road; they built two extras.
But the broadband incumbents have no incentive to build more capacity for those "toll" lanes; they don't have competition to deal with, so why bother? Who's going to leave? Where can you leave to? If you're lucky, you might have one other choice. But most people don't even have that.
So when they say there's some consumer benefit to this plan, that's a complete lie. For an eloquent statement of why, listen to candidate Barak Obama (who appointed the current head of the FCC, who's pushing this plan).
“I am a strong supporter of net neutrality.” Explaining, he said, “What you’ve been seeing is some lobbying that says that the servers and the various portals through which you’re getting information over the Internet should be able to be gatekeepers and to charge different rates to different Web sites…. And that I think destroys one of the best things about the Internet — which is that there is this incredible equality there.”
And that was dead on. Too bad he's completely forgotten what got him elected (the current situation with the intelligence agencies is another example of that).
The other part, which he didn't touch on, there, was that it also destroys the next Facebook, or Twitter, or Instagram, or Pinterest, or... The point is that it is heavily in favor of incumbents.
One example that I saw elsewhere (my apologies to the person who wrote it; I can't remember or find it now), was that it could completely destroy a new game, as it gets faced with lag (because the creator can't afford to get into the fast lanes) and can't offer a good experience, through no fault of its own.
So call your Congressmen and Senators, because this is a plan that benefits no one except the incumbents in a few industries. If there were real competition, this idea would be a non-starter, because consumers would immediately abandon any company which tried to implement it.
And when the FCC opens this for comments, give them comments. And put those comments in the form of a Word Document or PDF, as that will force the FCC to actually read them.