This point about donations comes up on literally every single one of these posts. Them throwing their wealth into the treasury maw would be a meaningless blip. They are arguing for the real systematic change that would bring in substantially more revenue than a few one time donations. Supposedly.
If that is true, though, then they're not actually talking about taxing them -- they're talking about taxing others more heavily too -- otherwise all of them donating would have the same effect as increasing their taxes.