suppose MWI is correct, now the counting patently doesn't work for probabilities
What is the correct counting for MWI, exactly?
does not account for potentially enormous number of simulated beings that can easily tell their reality is simulated as the simulator cuts some corners.
I think you are misunderstanding the SA, which is surprising since it's formally pretty simple.
The SA is a trilemma; finding evidence that strongly supports one leg of the trilemma is not a problem with the trilemma itself. It's just reasons for you to bite a particular bullet: "the SA says 'either X or Y or Z', and here our reality looks like a cutrate simulation, so I guess Z was right after all!'
So the trilemma remains 'watertight' even if the specific paper in enumerating reasons to believe X (or Y, or Z) fails to cover some favorite bit of reasoning of yours. The reasoning still fits inside the trilemma framework and is not an argument against the framework itself.
(My own impression is that your cutrate suggestion wouldn't go very far since it's not clear - to me, anyway - what a cutrate simulation would look like, and whether our own universe is not cutrate. One could validly argue that our failure to find good clear evidence that we're in a simulation is evidence against being in a simulation, but quantifying how much evidence this would be is even harder. And given how many crude simulation we run for science & business & pleasure, and the Fermi paradox, it seems especially unlikely that this point is strong enough to move someone from biting the we're-in-a-simulation bullet to biting one of the other bullets.)
I'm pretty sure all this movement will look very silly in 100 years - there will be dangers they did not see and there won't be dangers they focused on.
Everyone looks silly from 100 years on. That's not a useful point to make.
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.