Situations like this are extremely difficult to predict accurately. It could become a big problem. But it has a decent chance of blowing over.

The main issue is to harness the energy that the moderators currently put into their subreddit. They're not sad that CSS is going away. They're sad their toys are being taken away from them. That's not to trivialize it, not at all -- people like to tinker, and playing with your subreddit and putting your markings on it is a toy for adults. It's a game. It's necessary to replace that with something that feels equally deep and immersive.

Or, you know, just don't mess with the status quo. But if you're going to do it, I think that's why people are rebelling. Not because the functionality is gone, but because they're losing a creative outlet.

What's worse is that their new mobile site and their profile pages use more whitespace. A sign of things to come probably.

Making it beautiful with nice animations should come second and the mobile version still crash a few times a day for me.

Recently they added a useless interstitial.

It's interesting to me they say the app is faster; presumably they're artificially slowing the mobile site just to push app installs.

Reddit has a setting to disable custom CSS on subreddits, so it doesn't make sense why you'd force the subreddits not to have it.

Availability hueristic and personal bias. There are others.

CSS is a tool. Often, but not always misused.