100 years ago it would seem to have been too early to fund work on AI risk mitigation

Hilarious, and an unfairly effective argument. I'd like to know such people, who can entertain an idea that will still be tantalizing yet unresolved a century out.

that seems like an overly narrow choice reliant on presumption that it is not an alternative to not work on AI risk mitigation now.

Yes. I agree with everything else, too, with the caveat that SI is not the first organization to draw attention to AI risk) - not that you said so.