Before bl, it was slice of life/comedy strip comics that everyone complained about on here. A lot of it is purely done out of jealousy.
That aside, the BL hate is just a bit more intense because old school comic lovers with homophobic tendencies (that they will repeatedly deny) think it ruins their beloved artform. Or in many cases, people with purely homophobic intentions will chime in with arguments that disguise their intentions as just "caring about the site", "caring about the industry" or "wanting diversity".
Ironically these people are completely uninterested in diversity, and might even be against it, as soon as it shows up in mainstream media and their beloved publishers (marvel, dc, etc). That's when you get the "WHY DOES EVERYTHING NEED A GAY/POC/TRANS/WHATEVER CHARACTER" complaints. Stating that they are "not interested" and "stop shoving it in our faces and keep it where its wanted".
Well it's wanted on Tapas and Webtoon. And since it's gatekept out of other spaces to a large extent, creators and readers of BL will find each other there. But apparently these people aren't satisfied with that.
So we aren't allowed to exist in mainstream media.
We don't deserve to exist and flourish in indie media.
So... I guess the conclusion is just that we aren't allowed to exist, period. That's where these mentalities have ended up in the past and it's where they are bound to end up if they are not challenged and called out for what they are: homophobic and potentially dangerous.
BL makes a few people uncomfortable, yada yada... I would rather let those people be a bit uncomfortable than have gay creators face discrimination for their sake. Because honestly, their discomfort is their own fault and their own problem to deal with.
I apologize for any bad grammar in this post, it is very late and I am in the middle of a very tough work week, so I can barely form a proper sentence.