to all the people

TL;DR: defending Taesung... guys there's really nothing to defend. To all the people getting pissed at Taesung's actions and calling this toxic... what more did you expect?

Sorry this relationship isn't what you want to read. It is a toxic relationship. The author doesn't sugar coat it, and presents it as is. So stop reading this if you're hung up. There are manhwas out there with healthy relationships, go read those for vanilla and fluff. Not every relationship portrayed in fiction is going to be healthy. The author can do what they want.

In this context Taesung is a mafia boss. He's a ruthless, horrible person who's killed people, who leads a violent gang for god's sakes. He isn't going to just change himself in a snap. When such a possessive person has a lover who's 'goodness' keeps leading him into situations that get him hurt, he's bound to lose his patience. He's controlling. He tells Soo-young to stop getting himself hurt, but Soo-young can't help his own actions. Taesung wants that to stop, so in his warped view, he takes extreme measures thinking one big injury on Soo-young will teach Soo-young a lesson to stop.

Letting Soo-young be injured this time will stop future occurrences as Soo-young will think twice. I am not defending his actions. I'm merely saying things as they are, and if you expect Taesung to be any different... you're going to be disappointed.