I also just want to point out this is absolutely not an ‘internet only’ phenomenon. This has been a stereotype gay men have been fighting since time immemorial. (I do know the femme=passive butch=active partner thing is also prevalent in wlw spaces, but I have the most experience with it in mlm spaces).
Ever since straight people learned that some guys like to get things stuck up their ass they’ve sought to separate out the ‘effeminate gays’ (bottoms) from the ‘real men, they just wanna fuck’ (tops).
Pretty much throughout western history, if you were a man who fucked you were fine - you could mostly go about your day because like, you’re still just sticking your dick in a hole. But if you were the receiving partner, that was when laws of sodomy and social stigmas generally applied to you and affected your life. And this is where labeling someone by their sexual proclivities comes from.
Quite often men who fucked other men would still identify as straight and not participate as strongly in queer spaces, whereas men who generally preferred to be penetrated were the ones who occupied queer spaces, formed communities of queerness, and suffered the higher risk of social stigma, harassment, and being outcasts.
This is why knowing queer history is so so important. When people, be they in fandom or in real life, support things like ‘this man is a bottom, he is effeminate, he dresses a certain way, he gets pegged, he is soft and uwu and obviously that means he takes it up the ass’, they are perpetuating the same exact stereotypes that have plagued and harmed the mlm community for centuries.
Top =/= masculine. Bottom =/= feminine. There is no correlation between dominance, submission, or which sex acts are preferred by which types of sexual partners. (The number of times I have heard ‘he’s a top, he wouldn’t suck dick!’ Like…bruhv…..)
Also, someone being a completely 100% committed top or bottom is….extremely rare. I actually don’t think I’ve ever met someone who was 100% against playing a particular role if the circumstances are right. (Although everyone certainly has their preferences.)
Don’t let historical homophobia and the attempted emasculation of mlm men fool you, and especially if you’re young, remember that who and how someone fuck’s does not and should not define their place in any given community.
And, as the above addition points out - Top/Bottom dynamics are completely separate from Dominant/submissive dynamics. Usually, if someone on the internet thinks they’re talking about whether someone is a Top or Bottom, they’re usually actually talking about whether of not that person would be the submissive or dominant partner. While they can coincide, they absolutely do not have to.
(Which is a whole separate rant for an entirely separate post, but the gist is really the same in that the general beliefs of what makes a ‘Dom’ and what makes a ‘sub’ are so tied into the heterosexual binary that they become completely useless for actual Scene dynamics.)