
The author decided to show this scene for a reason. Seo in is testing boundaries and provoking. MC might be the only person that knows/truly cares and would reach out to help. If I saw my friend in that situation it would be a cry for help. Seo In is clearly dissatisfied with his current life, and MC might be a bacon of hope. Someone to help snap him out of it. It's easy to declare a character as "bad or evil" but there's much more nuance in real life. Think about how Seoin spiraled to this point and what he's truly showing.