Because the man called Kain Highwind is nothing but a foul traitor. He's attacked his own best friend, attempting to kill him. He aided in the kidnapping of his other best friend, a woman whom he lusts after in a disgusting manner. He's stolen from the rest of his allies, taunted and opposed them.

Even in his right mind, his answer to save his own friends is to harm and kidnap them. He's a disgrace.

[Welcome to the crash course in Kain Highwind's Dark History 101. Although it was technically he, the Dark Self, who did all the bad things, and the last part in his right mind was all done for good reasons... it doesn't matter right now. He's out to sabotage his true self however he can.]