Isn't that equivalent to setting the tax rate X% lower? The only problem I see otherwise is that it's not a progressive tax - 5% of a trailer is much more of a

Isn't that equivalent to setting the tax rate X% lower? The only problem I see otherwise is that it's not a progressive tax - 5% of a trailer is much more of a poor person's income than 5% of a mansion is of a rich person's. But for that you can use UBI or something to make any flat tax net-progressive.