And that folks is the fundamental social difference between Humans and Demons.
A solitary Human by itself is far weaker than a solitary Demon, but to make up for its own 'weakness', it groups together with other Humans to become a far stronger group, "Monkey together strong", this compels us to connect and help eachother in the name of survival, Iruma here isn't just feeling irritated and ill at the lack of selflessness because of his values, but also because of his Humanity.