the weird thing for me is I can stomach alot darker and gory things in regular video games , tv and movies but when it comes to this game it's too much for me. I think it's because of the facial expressions and emotions on the girls. In other forms of media I rarely see the facial expressions and emotions unless it's a movie or something but even then, the images of the emotions and expressions hit me way harder in this one for whatever reason.
It is just about empathy and how it is easier to be triggered.
Reading books or watching movie is like someone else's horrible shit. The author write it. In this game, or other VN, you are the one making the choice. It is not just a story. You choose to hurt someone. That makes it easier for us to have empathy. Making a choice means you are actively participating.
Also, the description is important. You can see the girls suffering. In many video games, you kill the people and they just gone. The game does not emphasis what's their emotion, except some important characters.
It is similar in real life. Why many people are fine with eating meat, but not eating dogs and cats. Often people no longer make connection between the meat they have and the animal itself. They do not need to kill the animal themselves. They do not see how the was killed. But some people will still feel wrong if they went to a farm and played with the cows, and then later tell them the dinner is the cow they played the afternoon.