You can always be a fan of something. Whether it is an artist, community figure, company, music group, (e)sports team, or whatever. There is nothing wrong with rooting for the things you like.
The problem is when it goes too far. Stans are what we call them usually for the worst offenders. But it is currently more prominent than ever due to social media.
Fans that for no reason protect someone, believe everything they say, or worst twist facts to make their idol better than they actually are. Why do they do this?
Well, because the fans have devoted their time to it. They follow their art, products, personality, content, or whatever and thus don't want to feel it was to waste. One of the worst feelings a human can have is to know that they wasted their time.
They go to any lengths to brainwash themselves and others that what they did was the right thing. One of the current examples is the ongoing issues at game development companies particularly Blizzard and Riot Games, where sexual- harassment and discrimination are present.
These cases led to many victims felt or were indeed assaulted (in some cases rape). Still, because they make popular games, the fans of the companies will protect them. They make comments like 'innocence until proven', or 'there is no public information so how can this be true. Basically, they already decided that it isn't true and attack the reports when it is literally a federal report.
Other examples are fans of music artists. Music artists usually make one or two great albums. There are only a few examples of music artists that keep evolving and make something better. But some fandoms that like a particular music artist, will go to the ends of the earth to 'prove' that their newest album is good. Even though, it was literally garbage. For example, they will say 'YOU jUST hAVe tO lISten tO iT MOrE', 'YoU Don'T UndERStand WhAT GoOD iS', or whatever to discredit the other party.
There are many more other examples, but it sickens me. They will twist facts and use buzz words like 'underrated', 'goat', 'revolutionary', or whatever just to make them feel better. Not anything about the product they consume or the entity they align with. No, just themselves.
Now, many things are overhyped for no reason. Disgusting entities and people get away with crimes. Morals and ethics are thrown away all for what? Only to brainwash yourself that you were right and never wrong.
Fandoms are a disease.