A system that only taxes spending fundamentally has problems in that the richer people can afford to save and invest.
The initial, flawed response to this issue would be to construct some "massive political and logistical complexity" in order to track everyone's income and spending and family situation and lots of other stuff too and calculate their VAT refunds based on some formula. The much simpler solution is to just give everyone the same amount of money. Poor people will spend some portion of it on sales taxes, and they'll use the rest for other purposes of their choosing. Slightly richer people will spend all of the UBI on sales taxes but will come out even. Slightly richer people will be able to offset some portion of their sales taxes. Really rich people won't even notice they got a UBI.
Perhaps you really meant that "massive political and logistical complexity" is required to get anything through the legislative process? After all, the more complicated it gets, the more places lobbyists can hide loot for their employers.
TL;DR: my fear with UBI is that unscrupulous people will do unfair things like significantly raise rent to eat into other people's free money thus leaving the poor in the same spot, more or less.
I don't claim to know anything about your town, but I've lived lots of places and in general, in order to really fuck people over the bastards first have to limit their freedom somehow. Are there only certain parts of town in which the poor are allowed to live? Has public transportation been limited in arbitrary ways? Do zoning regs or HOAs enforce impractical restrictions on housing? Would it be OK if your neighbor parked a mobile home and camper behind her house for her recently-divorced sister-in-law plus five kids? What if her nephew and his girlfriend also moved out back?
> A system that only taxes spending fundamentally has problems in that the richer people can afford to save and invest.
That is an existing problem inherent to any tax system. It's just saying "Rich people can afford to not spend all of their money". I don't see how that's fundamental to taxing only spending.
There are similar issues in agriculture subsidies and price regulation. E.g. High fructose corn syrup is probably as popular as it is because corn has been subsidized and cane sugar has a regulated (high) price. It's kind of like an inefficient arbitrage between physical goods to avoid taxes.
If you taxed only assets it wouldn't be a problem. Mo money mo taxes.
Whether you want to tax predominantly assets or spending usually reflects which side of the capital divide you see yourself identifying with - predominantly a recipient of unearned income (e.g. landlord/FIRE) or a payer (e.g. renter).
In this proposal, sales tax is the only tax. You can't run a government without money.
Lets say apples have a -5% tax rate, and cost $1. Every time I buy an apple from the store, I pay $0.95 (the government pays the rest, which is a problem in and of itself). I can sell that apple for $1, and the government basically just paid me $0.05 for selling an apple.
The problem with the government paying that $0.05 is that sales tax is assessed at time of purchase, but the government isn't there to pay their part. The grocery store basically has an IOU from the government. 5% may be higher than the grocery store's margins, which means the customer payment is actually less than the good is worth, so the grocery store's ledger actually goes down for that sale until the government pays back their part.
And then you have to deal with fraud. Nobody wants to overreport their sales tax, it costs them money. If you can make money off sales tax, people will filing fraudulent tax reports, and I really don't want the IRS having to track how many apples the grocery store actually sold. I'm sure money launderers would also find a way to use it to buffer their costs.
Subsidies probably still have fraud, but it's a smaller number of entities to work with. We can also budget for it because we determine the amount. I can give a budget to the subsidy, but I can't tell people to only buy 10,000 apples next year.