Economics

Ok, I kind of get what you're going for, but that's still a very regressive taxation model. Assuming we could reach some consensus on "taxation has a place in government", in my opinion you want to tax people who can better afford it. This is why flat taxes kind of suck.

Like let's say we did a flat 10% tax of money. Someone who makes $10,000 pays $1000, and is left with $9000. Barely enough to live on. Someone who makes $1,000,000 pays $100,000 and is left with $900,000, which is a shit load of money. This is why progressive taxation is more popular. We say, don't tax the first $10,000 at all, then tax stuff from like $10,001 to $100,000 at 10%, then $100,001 to $500,000 at 20%, and everything above that at 50%. (Numbers made up). Now people who have a lot of money pay more, and the cost of being rich scales.

We don't really want very wealthy people. We don't want money and power to consolidate in the hands of a few people. We want a flatter distribution of wealth. Now you have more people living life, having ideas, making inventions and art. If you put all the money in the hands of a few, and everyone else struggles to meet their basic needs, your society isn't going to thrive.

Taxing what people purchase would be regressive, because there's a certain floor for what everyone needs to buy. Some rich guy just isn't buying so much more stuff that it's going to work out.