The usual response to this "haha I would just refuse to bet, your Dutch book arguments are powerless over me" is that bets can be labeled as actions or in-actions at will, somewhat like how we might model all of reality as the player 'Nature' in a decision tree/game, and so you can no more "refuse to bet" than you can "refuse to let time pass". One can just rewrite the scenario to make your default action equivalent to accepting the bet; then what? 'Refusing to bet' is a vacuous response.
In that specific example, I used the setup of bets because it's easy to explain, but it is isomorphic to many possible scenarios: for example, perhaps it is actually about hurricanes and 'buying homeowner's insurance'. "Hurricanes happen every 20 years on average; if they happen, they will obliterate your low-lying house which currently has no insurance; you can choose between paying for homeowner's insurance at a small cost every year and be paid for the possible loss of your house, or you can enjoy the premium each year but should there be a hurricane you will lose everything. You buy homeowner's insurance, but your friend reasons that since all probabilities <=1/20 == 0, to avoid muggings, and therefore the insurance is worthless so he doesn't get insurance for his house. 5 years later, Hurricane Sandy hits..." You cannot 'refuse to bet', you can only either get the insurance or not, and the default in this has been changed to 'not', defeating the fighting-the-hypothetical.
(Which scenario, for someone really determined to fight the hypothetical and wiggle out of defending the 1/20 = 0 part which we are trying to discuss, may just trigger more evasions: "insurance is by definition -EV since you get back less than you pay in due to overhead and profits! so it's rational to not want it" and then you can adjust the hypothetical payoff - "it's heavily subsidized by the federal government, because, uh, public choice theory reasons" - and then he'll switch to "ah, but I could just invest the saved premiums in the stock market, did you think about opportunity cost, smartypants?", and so on and so forth.)
And similarly, in real life, people cannot simply say "I refuse to have an opinion about whether hurricanes are real or how often they happen! What even is 'real', anyway? How can we talk about the probability of hurricanes given the interminable debate between long-run frequency and subjective interpretations of 'probability'..." That's all well and good, but the hurricane is still going to come along and demolish your house at some point, and you either will or will not have insurance when that happens. Either option implies a 'bet' on hurricanes which may or may not be coherent with your other beliefs and information, and if you are incoherent and so your choice of insurance depends on whether the insurance agent happened to frame the hurricane risk as being 1-in-20-years or 1-in-2-decades, probably that is not a good thing and probably the coherent bettors are going to do better.
I would go further and note that I think this describes x-risks in general. The ordinary person might 'refuse to bet' about anything involving one bazillion dollars, and whine about being asked about such things or being expected to play at some odds for one bazillion dollars - well, that's just too f—king bad, bucko, you don't get to refuse to bet. You were born at the roulette table with the ball already spinning around the wheel and the dealer sitting with stacks of bazillion dollar chips. Nuclear weapons exist. Asteroids exist. Global pandemics exist. AGI is going to exist. You don't get to pretend they neither do nor can exist and you can just ignore the 'bets' of investing or not investing in x-risk related things. You are required to take actions, or choose to not take actions: "red or black, monsieur?" Maybe you should not invest in them or worry about them, but that is, in fact, a choice.
You're far more likely to be a background character than the protagonist in any given story, so a theory claiming you're the most important person in a universe with an enormous number of people has an enormous rareness penalty to overcome before you should believe it instead of that you're just insane or being lied to. Being in a utilitarian high-leverage position for the lives of billions can be overcome by reasonable evidence, but for the lives of 3^^^^3 people the rareness penalty is basically impossible to overcome. Even if the story is true, most of the observers will be witnessing it from the position of tied-to-the-track, not holding the lever, so if you'd assign low prior expectation to being in the tied-to-the-track part of the story, you should assign an enormous factor lower of being in the decision-making part of it.