Which shows once again that he is through and through a Slytherin.
You can pick any house in the series and you will find killers in it.
Being Slytherin doesn't mean you have to be an asshole, being Slytherin means you wanna climb the ranks of wizarding world and become the best. That can include backstabbing but it can also include friendship and comradery as it is evident with @Ominous Gaunt
Ominous embodied the perfect spirit of Slytherin house. Not Sebastian.
Ominous was ambitious and wanted to break the chains of tradition.
Sebastian good or bad still committed a crime!
Why should we just because he is "cool" accept that and give him a pass?
In order to use curses you need to wish harm upon the person you target it at.
Sebastian wanted to Torture
Sebastian wanted to Control
Sebastian wanted to Kill
Is this someone you wanna give a pass to?
A 15 year old boy that already tasted worst of humanity has to offer and didn't plan on stopping?
Would you have blood on your hands if he decided to take it further?
TAC did the right thing.
TAC cleared the street of a murdering power hungry wizard
It isn't a backstab, it is justice!