Fandom: Why do some fans care so much about how someone watches a show?

I can't stand when some fans try to tell other fans how they should be a fan. For instance, I saw where a fan posted this (I edited it to remove the show and ship): "when people think being a ___ fan means only watching it if ____ goes canon like if you like ___ cool okay I don't care but please don’t refer to yourself as a ___ fan as if you even watch the actual show it actually annoys me so much."

When Arrow originally aired, Laurel Lance/Black Canary was one of the main reasons I continued to watch the show. John Diggle and Thea Queen were the only other characters I liked. I didn't like this version of Oliver Queen/Green Arrow and I also didn't like Felicity Smoak and a lot of the other random characters that kept popping up on the show. The writing quality continued to go down each season, many of the storylines were terrible as well as focused too much time on Felicity or other random characters. Choosing to watch the show for Laurel, John and Thea didn't make me any less of an Arrow fan because I tuned in for those characters as opposed to all the other characters on the show. Which is why I don't let other fans speak for how I like or don't like something.

This type of fandom thinking makes no sense because there is no one way to be a fan or to watch a show. If you like only one or all the characters, a certain couple or all of them or none of them, certain seasons or all the seasons, etc. it doesn't change the fact that you are a fan. And no one should be able to define or determine why someone is a fan of a show. Why do they care why someone chooses to watch a show? They should watch a show their way and not worry or judge others for how they watch TV. Not everyone is going to like the same thing, so why expect people to watch TV the same way. Can't we just enjoy being a fan in our own way.