I was bullshitting in order to survive. Sorry, desperate times require desperate measures.
To be honest, Ultra was so dangerous that I have a feeling almost every scum might have wanted him dead, even those townread by him, just out of fear he might finally figure things out.
It's like you kill him when he townreads you, and you don't have to worry about him realizing anything. You can also use his townread as cred. (Monti didn't, so it's a plus for him.)
As Ali, I killed Monti (don’t remember his character from that game), even though he townread me. I did it because I preferred to kill him before he figured things out, and I didn’t want to have to discuss things with him.
Ultra was also hard to influence and was giving town order and structure in this game. Killing him gives scum the benefit of town becoming more chaotic and easier to influence.