Can you understand what Baek Ki-tae of Mead Inc. Korea did to his younger sister? (Spoiler)

‌He fights so desperately to protect his younger brother,
but he practically leaves his younger sister to fend for herself.
I was so furious that I felt like saying, "If we had just done exactly what my brother and older brother said and died, would this be the result?"
Even after seeing his sister become a drug addict, Baek Ki-tae only tries to avoid responsibility.
Baek Ki-tae is the one who made Baek So-young a "medicine peddler," and he's the one who tacitly allowed her to date Kang Dae-il just to control him.
The only unexpected part was that Baek So-young and Kang Dae-il actually loved each other, and Kang Dae-il even committed suicide to protect her until the very end.
How can he act like everything is fine after leaving so many massive holes in his sister's heart;;;
Especially now that she knows her brother was the one who caused Kang Dae-il's death;;;
I mean, even Mexican drug cartel bosses tell their families never to do drugs, yet they do it themselves.