Your reasoning makes sense under a regime of infinite games. In other words, the goal is to continue playing the game rather than win once.
These people do not believe we are in an infinite game. They believe they have a narrow set of moves to avoid checkmate, and apparently getting rid of Sam Altman is one of them.
I will suggest another reason though: we are likely already in the light cone of continued AI development. So none of the vigilante actions are justified under their own logic. It’s probably preferable to avoid being in jail when the robot apocalypse comes.
I don’t think the death of Sam Altman or even the dissolution of OpenAI would stop the continuation of AI development. There are too many actors involved, and too many companies and nation states invested in continuing AI development. Even Eliezer Yudkowsky became president of the United States he could not stop it.
Eliezer Yudkowsky has gone so far as to say that it might be ok to kill most of humanity (excepting a "viable reproduction population") to stop AI. If that's not just talk, then this line reasoning only gives you a few possible modes of action. I would not be worried about the people with Molotov cocktails, but I'd be very worried about bio terrorism.