The only time I've encountered people that care a little too much about what distro is being used, is right after having transitioned to Linux; the sheer liberating potential of the thing can make you lose your head.

I've come across a lot of professional bias about Linux distros, but that's usually due to real-world experience with tough or bad projects. Some times, decisions are made that make a given distro the villain or even the hero of the story. In the end, you'll hear a lot of praise and hate, but context absolutely matters.

There's also the very natural tendency to seek external validation for your actions/decisions. But some people just can't self-actualize in a way that's healthy. Sprinkle a little personal insecurity into the mix and presto: "someone is getting on great with that other Linux I don't use, so Imma get big mad."