A lot of people here criticised the scumbag for his shitty attitude, but such an appearance is only a matter of time as Sayu must face with her past influence one way or another, which will strengthen the relationships between the main duo. I personally find it sad that a question answered in chapter 9 is raised again here. For a lot of people, "unconditional kindness" is some kind of magic, and they apparently have lived such a "logical" life that they reject this "abnormality". Maybe they don't even understand what "logical" actually means.
One more thing, with the way things have turned out, I think the plot from onwards will present more disturbing elements. Not really to my taste but it's still interesting at least.