Important Fandom Things to Remember
There really isn’t such a thing as “coming late to a fandom”. I know we all joke about it. But different people get involved with different things at different stages in their lives for different reasons. No one is more or less of a fan because they haven’t been following the fandom since pre-release or whatever. It doesn’t matter how much more knowledge or fandom know how you have--it doesn’t make you an inch more of a fan than anyone else, “casual” or no. Get off that high horse before you break your neck.
It doesn’t matter how popular a headcanon is, not everyone has to incorporate it into their fanart/fanfiction/etc (*cough* to cater to you *cough*). You can’t get mad at people for not having the same headcanons. It doesn’t matter whether those headcanons serve to make the characters more diverse...if it isn’t canon you can’t get mad at people for not going along with it. You can definitely get mad at them for erasing diversity in canon--but don’t be so petty as to get angry and self-righteous over them depicting characters as they appear in canon. You’re not helping your cause.
Alternately, you can’t get mad for people having headcanons or “alternate versions” that make characters more diverse just because “they aren’t [x] in canon”--that’s why it’s called a headcanon or fan theory you big lump.
On a similar note, you also can’t get mad at people over ships just because you have a “conflicting” ship or because the character(s) have canon pairings that are different or any other petty reason. I can understand being upset by pairings involving an adult and a minor...but most of the time ship wars are just the dumbest source of fandom drama ever. It costs zero dollars to ignore.
If your fandom has “multiple gens” then don’t fight over which gen is better. A lot of people’s reasons for preferring one over the other is because of familiarity and nostalgia (like which gen you were first introduced to and that got you into the franchise). You can say “[x] gen is my favorite” but don’t press that it’s THE BEST and anyone who disagrees is on your shitlist.
Just because the majority of a certain fandom is seen as “crazy” that doesn’t mean you can’t enjoy the show/video game/comic/etc. Just ignore the other fans.
Just because a show/video game/comic/etc has problematic content (like wow everything because nothing is pure or completely perfect)--doesn’t mean the fans are all complicit and ignore its flaws. We can all enjoy some media/entertainment while acknowledging there are some things wrong with it. It’s just not all of us are constantly writing essays about it. Don’t shit on people for liking something you don’t.
It doesn’t matter how irredeemable you think something is, you don’t have a right to tell other people they’re terrible human beings for not “canceling” it also. What are you the purity police?
TL;DR: Being in a fandom and interacting/creating fan content is all great fun. But you the moment you start having a “my way or the highway” mentality then you’re going to start having a bad time instead and suddenly no one wants to RP with you and your one-dimensional OCs. It’ll be like playing chess with yourself.