Umm

Erm, no one has insulted anyone who didn't like incest/twincest in the comment section. Only calm opinion sharing, that's all.
Unless you're considering that thumbs down are a sign of disrespect? In that case, sorry but that's not disrespect towards the ones who don't like twincest, it's only a disagreement with their comment.
As for the "warning" you would have appreciated, who did you want it from? The author themselves? The scanlator? The fanbase? (For the latter, scrolling the comments before reading would have been the biggest and best warning).

I would appreciate it better if they put a warning at Summary.
Such as "chapter 3 about twincest"

The fact that I and others get massively down voted just because we don't like incest/twincest, shows how hostile people are towards others who don't share their opinion.
There are certain things I don't like to read and I would appreciate it if the scanlators (as a card before the manga) or the person who uploads it here (as one sentence in the description) would give me a heads up. I don't like to read the comments before reading a chapter, as they usually spoil too much. I typically read the tags to get a general idea, but as only the third chapter contained twincest, I was too early for them to change.

no disrespect...but by the 2nd page I knew the 3rd chapter was going to be twincest. Without reading comments or seeing a tag or having a note from the scanlators. Some manga come as a surprise, but this one was obvious from the getgo. There are certain types I don't like to read...and if I start reading one and realize that it's going in that direction, I'll stop reading it.
And sorry you feel people are being hostile to you by them downvoting you. But I honestly don't think anyone was trying to disrespect you or any others who don't like to read this type of yaoi.

I did stop reading it after page 2 actually. However it's still nice to know beforehand.

To the other point, it just made me sad to see all these other people who where down voted just because they didn't like the chapter. Like Wee-Wee Lollipop pointed out it was "only a calm opinion sharing".