> future employees most likely won't be pure idealists who will take a lower pay out of the satisfaction that their work helped others
If you rewrite that to "a much smaller percentage of prospective future employees won't be pure idealists..." then I would agree. But it's about the pool being smaller, and in fact small enough that you risk not being able to find anybody, but the fact that 95% of people are not going to be adequately motivated by helping underserved people does not mean that the remaining 5% won't be.
Existence proof: I am working for substantially less salary than I could get elsewhere. I can prove it, I've been offered the higher salary at a FAANG and turned it down twice. It's financially irrational. I don't think it's wrong for people to work for directly ad-funded Big Tech. Or even for me. I'm not ecstatically happy in my current position. If I were younger I might make a different choice.
But I care enough about working for a mission-driven organization that I basically have no intention of leaving as long as the organization doesn't lose my trust about being mission driven. (There's often a gap between stated positions and reality, and I try to watch closely to monitor how big that gap is.) And I think I'm far from being the only one in this position.
I'm also aware that it's a privilege to even have the option. I grew up poor. Now I have a spouse and kids and live in an insanely high CoL area that we mostly don't get much from, but our past work was enough to make us financially comfortable. (Actually, I suspect it probably has more to do with the extremely unfair macroeconomic situation that has inflated our real estate and other investments, but whatever.) When I go to feed the worms, I won't be leaving my kids with as much financial security as I could have, but I hope to leave them with better respect for my values than I would have otherwise.
That said, "mission-driven" doesn't actually mean that much. Any mission is going to have unintended consequences, and it's pretty dispiriting what people are actually using my mission-driven labor for. There's no easy way to sort companies into "good" vs "bad". It's often not even a meaningful distinction at a whole-company level. But there are still large differences if you pay attention.