We're encountering several little phenomena here.

Many of the people who were passionate or concerned about this issue are here and elsewhere - but they're no longer on reddit. The anti-protesters are those who didn't understand, didn't care, and are just annoyed that their opium hit is suddenly asking them to give a shit. They're consumers, and in the absence of those who care, they've gotten bolder and a larger proportion of representation on the site. In the ~2 times I have checked in on Reddit, I've noticed a drop in comment quality.
This is a classic Conservative reaction. Not exactly the Donkey/Elephant kind, but that raw conservative instinct endemic to humanity. It's the fear that change is a zero-sum game, where is people move up, other's status degrade, or if it doesn't. that someone will create a new environment that they themselves are less familiar and adept at navigating. Some people are so insecure that they'll lash out at anyone as long as it makes them just sit still in their chairs, please. These people are fear-driven ghouls, it could have been anything and you'd get a similar reaction.