Because Argos is a good boy and did nothing wrong. You will understand if you play the ruthless chapters.
see, that’s the thing. The ruthless route exists, you can be a dick to Asterion. I think I should therefore be able to ruthless to Argos. All Argos had to do to avoid this reaction would be to give me the mirror as a show of good faith and use the wine as a bargaining chip later instead. At least, that’s what I would do if I wanted to manipulate me.