I don't like it as a warning. I don't mind it as a content tag... but the idea that people need to be warned and kept safe is... uncomfortable. Completely not what is intended mind you. But yeah... really uncomfortable when you think about it that way.
I have several comics that I could throw the BL title on and get away with it because the content is there. I just don't, because though applicable and often an important a part of the characters or story it's not the story's complete focus or theme.
I DID however, put it on a comic that I put under the romance genre, and this was a really huge personal debate for myself, cause I really do not enjoy the label and how it's either used as a 'warning', or a 'click bait' move. But I also do not mind it as a tag. If it's applicable to the content.
This is because the comic in question is under the romance label, which is almost it's own storytelling beast with it's own genres, couplings and kinks. It's a whole new mess. People who go through the romance sections specifically look for the type of romance they are interested in and the labels are more acceptable. They always have been, it generally where these labels originated and drifted off eventually showing up on comics outside the romance genre. This even more true if you're looking for COUGH COUGH smut.
If you're looking for BDSM you're gonna be looking for series tagged with that, same goes for other tags such as BL or GL. Romance readers are not looking for LGBT+ content in general they're looking for a specific type of relationship they want to right now feed off of, it's why you get those weird as heck 'shipping names' in fandoms. They're tags and labels to find a very specific type of relationship that the fan would like to find content of (and this goes for people looking for romances about straight couples as well)
So my thoughts on the BL tag, they're complicated, clearly. My thoughts on BL content even more so because I do not like fetishism of a lifestyle, which is what a lot of comics under the BL title like to do (not all of them, but very large and unfortunate amount) so I tend to avoid the BL tag. Which does not mean I don't like LGBT+ content. I do, I look for it, I LIKE finding stories I can relate to on that kind of level. I just do not like the horrible 'looks at the hot guys fuck because it's HOT' content.