The scary images of tiered Internet packages from Portugal and Indonesia that are being passed around are also about zero-rating. They are really no different from mobile plans we have in the US, except that their advertising happens to be more brutally honest.
People like net neutrality as an abstract principle when it's described to them, but many people will gladly personally give it up to watch a TV series.
To be clear, I think this is a bad thing. I think zero-rating is anti-competitive. But there are people who love it. That's what it means to be against net neutrality.
However it is super duper lame that a ton of politicians blindly follow party lines. Sigh.
But leaving that aside, I didn't say all Republicans are against Net Neutrality. I'm sure some are in favor of it, just like you can find the odd pro-choice or gay Republican. But the Republican Party as a whole is against NN, and has been very vocal about wanting to get rid of it. Republicans said "If we get elected we're going to get rid of Net Neutrality," and then they got elected. So, you know, no surprise here.