A lot of people are emotionally reliant on this game to an unhealthy extent. When you criticize the game, they feel you are criticizing the very foundation of their happiness. Every MMO kinda has this to some extent, but for some reason it's more predominant on FFXIV than anything else I've played.

It's also an entry in a storied franchise with a long history of extreme fanboy culture.

There's a lot I could say on this topic, but I'm not convinced spreading awareness of the issue and trying to understand it will do anything to fix the problem.

If you're interested in reasonable discourse about the game, tertiary communities like r/FFXIVdiscussion have cropped up to give people access to a more reasonable platform. Otherwise, you just kind of have to learn to laugh at all the strange people and take it in stride.