As far as paying for more bandwidth. Political groups advertise on sites like YouTube and Facebook. The ads are then hosted on those servers, or at least served up by them. How would a campaign get "extra bandwidth?". I mean wouldn't they be paying Facebook, not the ISP? Besides which Facebook was trying to bring subsided internet to underserved markets until those governments bought the lie that net neutrality is a good thing.
Would facebook buying their way into the fast lane that a startup social media site can't afford be covered by anti-trust laws? I mean, I suppose it's a competitive advantage, but not much more than owning your own server farm and a huge software development team is. And isn't that kind of the point of a tiered internet anyway?
In any case, not everything is hosted on youtube and facebook, and those companies would probably be able to afford the fast lane already anyway. There are other possibilities. As I pointed out above, climate change deniers and other such groups often run their own websites and blogs. Breaking net neutrality could be advantageous for small groups backed by wealthy industries.
Imagine I am someone who doesn't know much about science. I click on three google links because I want to look something up about a controversial subject. One is a denier site that is on the fast lane and highly responsive. The rest are volunteer science based outlets that take forever to load because they are not on the fast lane. Considering I am not a very patient person, which one am I more likely to come back to in the future?
Imagine that your ISP is run by radical vegans. They could easily systematically favor vegan websites and slow down traffic to meat industry websites. Or maybe they'll just decide to charge an extra, small fee for traffic to meat industry websites. And hey, look, suddenly it's not just the meat industry websites that get less responsive, but also websites hosting ads for the meat industry. Pretty soon, no one is hosting meat industry ads anymore and every site has snappy, pro-vegan banners. This is not a case of monopolistic competition, since they are not in the business of selling meat (or meat substitute) products, and so they are not competitors to those websites; they are merely the ones allocating their bandwidth, and they happen to like vegan products.
Or maybe I own a large ISP and I just fucking hate people from Chesterton, IN, because this guy once gave me a wedgie when I was an awkward nerd in high school, and he was from Chesterton. And hey, look, some asshole started a Chesterton-based server farm! Fuck that Chesterton guy! I'm charging 10 cents extra for every MB downloaded from or to any server located in Chesterton! I don't have a financial stake in this. I don't own a rival server farm. I just hate those guys. Am I in breach of antitrust? Who cares, anyway? Chesterton is tiny. The vast majority of my customers aren't even going to notice. But maybe that tiny percentage of people who are actually from Chesterton and who are relying on traffic from elsewhere for their income will notice. And maybe that guy will have to relocate his server farm away from dirty old Chesterton or go out of business.
Silly example, I know. But now imagine that instead of people from Chesterton, I just hate Arabs, and I decide to charge extra for traffic to and from servers located in Arabic nations. Or maybe I hate Jews. Or black people. Or Chinese. Or maybe I just hate Republicans, so blue states get a discounted rate.
Or, imagine I am an ISP owned, via a number of intermediaries, by Russian oligarchs who want to influence an election by using, oh, I dunno, a network of internet trolls, message boards, and blogs to quickly spread misinformation around the globe. Well, I think you see where this is going.
Basically, the issue is that, when your ISP can decide who to favor on the internet in any way, the ISP can decide where you can and cannot go, or how easily and cheaply you can go there. With the internet being as influential as it is, on societal scales, that can affect how people behave in pretty dramatic ways. Do you want to give ISPs that kind of power? Are you going to switch ISPs every time you notice a certain website is slow or unreachable? Will you switch ISPs because they charge more for traffic to or from the Ukraine, or would it be easier just to visit a Russian website that has almost the same stuff (except for those pro-Putin blurbs they do)?