Presumably that money goes back into the pockets of everyday people who then spend it in an ever revolving churn of money which keeps capitalism working.

If your economy is held up by rich people and rich people alone, your economy probably sucks.

What exactly makes 'rich people's money' a finite resource? Where do you think their money comes from? If you look at the average billionaire, their wealth trends up even if they're giving big chunks of it away - Bill Gates is richer now than he was when he started giving away huge piles of his money, because for a rich person wealth is (unless you're literally lighting it on fire) not trivially exhaustible.

Many countries previously have had high tax rates on the rich (upwards of 50%) and those rich people still managed to avoid being poor.

It would be another matter if their plan was proposing to cut off rich people's income - but their plan doesn't even touch rich people, it is funded by corporations. Even if you were to institute a 2% wealth tax to fund public internet, the rich would still stay very, very rich because it's possible to keep earning money off your remaining wealth through investments and other means.