People mostly got mad cuz Yumin's bloodline will go extinct with those dominant Tiger genes, so there won't be anymore black footed cats...
They got mad because it's simply a completely different situation from when Yumin wanted to baby trap Taejun, cuz that was to keep the bloodline.
And they probably got mad because there are so many dumb readers who are too stupid to understand this.

Both of them wants each other to get pregnant. People were hating on taejun on the last chapter cause he seemed like he was gonna drug yumin, but let's be honest, yumin isn't really any better. Bro wanted to impregnate teajun the moment he met him. It's toxic, yes, but if their goal is to just have a child with each other then it's not even as bad as other mangas where the uke actually didn't want babies.
Yumin can just get pregnant and taejun can keep him by his side and Yumin can continue their family lineage so it's a win win for their situations ig