SI being the only one ought to lower your probability that this whole enterprise is worthwhile in any way.
With regards to the 'message', i think you grossly over estimate value of a rather easy insight that anyone who has watched Terminator could have. With regards to "rationally discussing", what I have seen so far here is pure rationalization and very little, if any, rationality. What the SI has on the track record is, once again, a lot of rationalizations and not enough rationality to even have had an accountant through it's first 10 years and first over 2 millions dollars in other people's money.
Note that that second paragraph is one of Holden Karnofsky's objections to SIAI: a high opinion of its own rationality that is not so far substantiable from the outside view.
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.