That's looking at the situation too simplistically. Stuff is produced when there is demand for it. When people have less money to spend, there is less demand.

That's looking at the situation too simplistically. Stuff is produced when there is demand for it. When people have less money to spend, there is less demand. If this tax puts more money in the hands of the bottom 90%—and especially the bottom 50%—it will increase their buying power, which will increase demand, which means that, in all likelihood, more goods will be created for them to buy. ...I think it's also worth noting that for the vast, vast majority of people, what's standing in the way of them buying stuff is not the lack of stuff available to buy: it's lack of funds to buy it with. So on that front, too, your analysis doesn't really hold true.