Yudkowsky's personal estimates of the probability of superhuman AI and the probability of his own research institution fixing it may have been more confident than most people's but he and his followers are no stranger to presenting Pascals' wager arguments to people who doubt approaches are feasible (even more so when it comes to stuff he isn't working on like cryonics), along with more explicitly Pascal-esque stuff like intertemporal bargaining with future AIs, simulations and infinite rewards/punishments...
But I think the argument for a policymaker or ML researcher to be worrying about this is at least better than Pascal's Wager (and remains so whether or not you buy any particular whiff-of-Pascal claims about simulations, "acausal trade", etc).
Someone who's primarily famous for an argument that would have been equally true and perfectly wrong at every past point in human history is someone whose opinion should be discounted via every available mechanism at your disposal.
To be clear, I have no idea what argument you believe Bostrom is most famous for and hold no particular brief for him as a thinker. But, repeating myself, the AI risk argument that he makes in Superintelligence and that Yudkowsky etc make is one that assigns a high probability to disaster. It's not a secularized Pascal's Wager based on multiplying a low probability by dubious infinities.
The AI singularity that Yudkowsky cultists worry about is more akin to “What if there’s a 0.0000001% chance there are aliens coming to attack Earth like in Independence Day?”