I'm not trying to attack you specifically, but I think some people get way too defensive about comments that don't just lavish praise. People are allowed to comment on aspects they don't like. It's actually useful, too - others who, for example, don't particularly get into hyper-feminine ukes like this one can read the comments, and be forewarned. They might decide to "just move along." Or other comments might say that the sex scenes are hot, so in spite of something they don't love, they might decide to give it a go - but at least they know going in that they might not like the character style. Hundreds of comments just going "OMG it's so cyuuuuute cinnamon roll squee" aren't very useful. Constructive/informative criticism is healthy!
Exactly. People who do not enjoy hyper-sensitive uses SHOULD move along, as you suggested. but they haven't been. I've yet to see any 'constructive criticism' so far pertaining to the art style, and I've only seen horribly offensive comments. For example, one person commented that the art style appeared so effeminate, why did the author even 'bother to make them male'. I found it horribly offensive that they wanted to misgender these characters based on their appearance. I saw another comment refer to them as 'lesbians'.
I love constructive criticism. I welcome it (and no, I don't mind cinnamon roll comments either).
But the audience, so far, has failed at that.
I don't entirely agree that they're "misgendering" him, because I feel that the creator has deliberately made him ambiguous, gender-wise. I agree that the comments you found offensive don't sound constructive - some people might find them informative, though.
To be more constructive about it, WHY has the creator chosen to draw him this way? It serves no purpose for the plot so far - he could just as easily have looked a different way, without it impacting the story at all. So, it was a choice purely based on preferred style. And, although sometimes this is because of the censoring rules I'm guessing, his "feminine" body type is often highlighted and accentuated by the creator's artistic choices.
Now, this stereotypical dimorphic style (tiny, 'feminine' uke; huge, 'masculine' seme) is a common part of why some yaoi is almost offensively heteronormative. So I can understand why some people are sick of it. This work is a part of a large body of works in the same genre that involves a set of conventions, so it can be judged as a part of that genre and those conventions, not just as an individual work.
To be honest, a lot of positive comments have nothing constructive about them, so I think it's unfair to expect all negative comments to be constructive. Having said that, constructive comments are usually more interesting. (Comedy excepted.) Personally, I'd always rather NOT offend anyone. It's a bit difficult to avoid though, because some people really do seem to get offended by anything even slightly critical, constructive or otherwise (I'm not saying you're one of them though!).
As far as the feminine styling, it is, as you said, creator's choice to be ambiguous. and there really is nothing wrong with that. my issue is people with WITH issue with that. I could quote more particularly ignorant comments, but I believe I made my point in previous comments so I will not be going over them again. agree to disagree when it comes to constructive comments, negative versus positive. I believe negative comments DO need to be more constructive than positive comments, as no one is stepping on any toes with with 'look, he cute and smol' comments. Constructive explanation is important particularly if you are leaving a comment that could be offensive, something that is not necessary with positive comments. (In my personal opinion, it just creates a bad community if people are dropping ignorant words, which is why I occasionally tend to point it out, but that is just my opinion).
as far as this style seemingly heteronormative, small vs. large, however anyone wants to put it, I can see your point there. I don't know much/ have thought about the trope. personally, it doesn't bother me, though I can see how some might be sick of the stereotype. to be honest, I don't see that changing anytime soon, but I hope more reads are available to those who would prefer a more equal playing field with the uke/seme.
(no problems with leaving long comments lol, it's cool :)

I actually really enjoy this art style, and these characters, and this manhwa.
If you aren't into it, it would be better to just move along instead of leaving nasty comments. no one is forcing you to read it.