It has to also be probable that their work averts those risks, which seem incredibly improbable by any reasonable estimate. If the alternative Earth was to adopt a strategy of ignoring prophetic groups of 'idea guys' similar to SI and ignore their pleads for donations so that they can hire competent researchers to pursue their ideas, I do not think that such decision would have increased the risk by more than a miniscule amount.
This kind of seems like political slander to me. Maybe I'm miscalibrated? But it seems like you're thinking of "reasonable estimates" as things produced by groups or factions, treating SI as a single "estimate" in this sense, and lumping them with a vaguely negative but non-specified reference class of "prophetic groups".
The packaged claims function to reduce SI's organizational credibility, and yet it references no external evidence and makes no testable claims. For your "prophetic groups" reference class, does...
Nick Szabo on acting on extremely long odds with claimed high payoffs:
Beware of what I call Pascal's scams: movements or belief systems that ask you to hope for or worry about very improbable outcomes that could have very large positive or negative consequences. (The name comes of course from the infinite-reward Wager proposed by Pascal: these days the large-but-finite versions are far more pernicious). Naive expected value reasoning implies that they are worth the effort: if the odds are 1 in 1,000 that I could win $1 billion, and I am risk and time neutral, then I should expend up to nearly $1 million dollars worth of effort to gain this boon. The problems with these beliefs tend to be at least threefold, all stemming from the general uncertainty, i.e. the poor information or lack of information, from which we abstracted the low probability estimate in the first place: because in the messy real world the low probability estimate is almost always due to low or poor evidence rather than being a lottery with well-defined odds.
Nick clarifies in the comments that he is indeed talking about singularitarians, including his GMU colleague Robin Hanson. This post appears to revisit a comment on an earlier post:
In other words, just because one comes up with quasi-plausible catastrophic scenarios does not put the burden of proof on the skeptics to debunk them or else cough up substantial funds to supposedly combat these alleged threats.