I can't help but believe that either Kirishima is being sarcastic or is tired of something related to yu's. . . Or his "Meet and Fuck: Yu Edition" became too popular for his liking and now he's trying to traumatize those who liked it with this works.
It is in my opinion that it was there all along, just how Waita Uziga showed glimpses of his true interests back when he did comedy/gag manga, although I hear he did contribute to some bizarre publications under other names.
Besides, you cannot feel anything besides schadenfreude if the character is unlikeable. If the character is noble, cute and likeable, the shock value increases, just how people are horrified when they hear of a little girl being hit by a car, compared to when you hear a drunk drowning in a river.
Think it's always kind of been there. I do agree its' been ramped up a bit as of late, but seeing as how it's the christmas season in japan I wouldn't be surprised if there are some pent up anger in there.