Taxes are either regressive, proportional, or progressive; flat and progressive are the same thing. While some (many?) consider proportional to be a separate category, I would argue that it’s inherently regressive, as any fixed percentage is going to come disproportionately from non-disposable income for any lower income individuals. Sales taxes are considered regressive because of this and they are a flat rate for most purchases.

You can make the argument that people have to buy stuff to exist, but they don’t have to purchase a home, but given the alternative is renting which impacts lower income people even worse, this seems like a specious argument.

Even with property tax, insurance, repairs, and mortgage, I’m paying less per month than people renting much smaller apartments in my area. Thats neither fair nor right.