As I said before, I don't like it because it's used more as a warning label than a content title. Using it as a title to content is one thing, but a good amount of people use it as a warning, complete with a warning message in the description. Example = "WARNING THIS COMIC IS BL. THAT MEANS THERE WILL BE HOMOSEXUAL MALE ON MALE CONTENT. DO NOT READ IF IT OFFENDS YOU." That right there. Not a label, it's a flat out warning, and it's insulting. Which is a hundred times worse when they include a "THERE IS NO SEX THOUGH JUST GUYS IN RELATIONSHIPS WITH GUYS" in the warning, because at this point your not warning us 'oh no, look out gay sex don't look if you don't like gay sex' it's 'oh no, a guy has feelings for a guy and that's just as shocking as sex and needs to be highlighted with a friggen warning'. I understand it's in most cases trying to limit flames and negative comments but you're still treating a 'relationship type' like something that might actually harm someone, and that's wrong. Especially when such titles and warnings are not needed or considered for relationships that are not gay.
Again if it's not sex, if it's just a relationship, I believe its not something you should have to be warned about (though I understand why people do it when it comes to trying to avoid hate comments). And again, as I explained before, when I do see it as a warning I automatically thin 'this is an adult/porn/smut series and I'm not interested in that so I'm gonna skip it.' Even though I know BL comics are NOT all smut. This is more so probably because in my experience with dealing with adult art these labels are usually only something you bother to put on porn art/porn comics/porn fiction, so that readers can quickly find the kink they are looking for at the time (not to sound vulgar, but usually people in the mood want exactly the porn they want right now and don't have time to go skipping about hoping to run into the type of porn they are looking for) so you get labels like '18+ Light Censorship', or '18+ UNCENSORED', or 'M/F' or 'F/F' or 'M/M' or 'M/F' or 'M/M/T/M/F' 'gore' 'incest' 'feet' 'some other thing that can be turned into a fetish porn you get the idea' Usually the titles are for porn, because that's when the content like that maters because the creators are catering to specific sexual kinks (it's also not exclusive to homosexuality. Again though, everything is labeled, and usually with more than one label, because it NEEDS to be.
I think the issue is more of an issue because most authors outside of pron do not label relationships that are not gay, if everything had a label I would probably see it as exactly that, a label and not a warning.
A light hearted story about a high school boy getting a crush no his male classmate that ends shortly after confessing and maybe a kiss does not need a kink warning.