If they're good enough to be hired to palantir as an engineer, I very much doubt at any point they were desperate.

You're missing my point. If all 'ethical' companies treat all ex-employees of 'unethical companies' as unemployable, they are effectively only going to work at 'unethical companies' regardless of whatever mindset has shifted over time.

I agree they shouldn't become outcasts, but it feels disingenuous to say that the reason for wanting to work for palantir is anything but "they wanted A LOT of money".

It's kind of beside the point. You could argue the change of mind/heart is unlikely, but if indeed they had changed, it would be better to encourage that. Perhaps they were lured by the money, or perhaps some jingoistic impulse, but then the reality of what the company was doing became clearer? Or their world view evolved?

That said, if some ex-Palantir worker was somehow working for UNICEF – to take an extreme example – it would be a little awkward unless they had denounced their old company in a fairly public manner.