It makes sense that YH fans are rattled by the recent development in the manga.
Like most LGBTQ folks they require attention for some reason, they want to be seen that we are out here.
Snk/Aot is one or the biggest anime title out there with mass appeals. Any representation of LGBT in this franchisee is a sweet delight for them.
Now imagine lesbian source of representation i.e. Historia being impregnated by a man for whatever reason. All their hopes and dreams done and dusted into oblivion. If EH is even remotely suggested to have a relationship then People are gonna remember this manga for the pairing ErenxHistoria aside from Story and characters, since Eren is the main character and his words and action carry weight in the franchise.
Ymir will be reduced to just another character that came and went out.
Thanks to this a large portion of LGBTQ hate on Eren. If Eren is confirmed to be hetrosexual then the following ships will be sunk>EM (possibly the biggest hetro fanbase)>LE (second most shipped yaoi pairing after ErwinLevi)>YH (possibly the biggest Yuri pairing, with lots of stakes)>ErenArmin(Thrid biggest yaoi ship, but relatively calm agiant Eren)>ErenAnnie (Very few shippers are left and have migrated to EH boat)
You see it's all a chaos ladder.