Do you buy the argument that we should take the ~10^50 future people the universe could support into our expected utility calculations?

Yes, I buy this argument.

If so, then it is hard to see how anything other than existential risks matters.

The question is just whether donating to an existential risk charity is the best way to avert existential risk.

•I believe that political instability is conducive to certain groups desperately racing to produce and utilize powerful technologies. This points in the direction of promotion of political stability reducing existential risk.

•I believe that when people are leading lives that they find more fulfilling, they make better decisions, so that improving quality of life reduces existential risk

•I believe that (all else being equal), economic growth reduces "existential risk in the broad sense." By this I mean that economic growth may prevent astronomical waste.

Of course, as a heuristic it's more important that technologies develop safely than that they develop quickly, but one could still imagine that at some point, the marginal value of an extra dollar spent on existential risk research drops so low that speeding up economic growth is a better use of money.

•Of the above three points, the first two are more compelling than the third, but the third could still play a role, and I believe that there's a correlation between each pair of political stability, quality of life, and economic growth, so that it's possible to address the three simultaneously.

•As I said above, at the margin I think that a good charity devoted to studying existential risk should be getting more funding, but at present I do not believe that a good charity devoted to studying existential risk could cost effectively absorb arbitrarily many dollars.