I don't think that's the case. Instead, it's just that the "let's tax the rich people more!!" idea is ill-founded to begin with, and the easiest way to show that is to point out that if instead of just taking some percentage more, you took everything they have, it still wouldn't solve the problem, not by a longshot.
Choosing some arbitrarily small segment of the population and saying "See, they don't have enough money to fund this program" is not the steelman you seem to think it is. Instead, try discussing something serious, like a plausible adjustment to the progressive tax system.
Nah, if someone puts forth an argument that is fundamentally flawed, it's neither wrong to point it out nor on me to do their thinking for them.
That said, if we want to talk taxes, I think a progressive tax system is nearly always wrong, immoral, and unfair, so you probably would disagree with any adjustments I'd suggest. :)
