[loeg]

As a creditor, you're obligated to pay taxes as if you charged a fair market rate, regardless of what you actually charge the debtor. So the actual floor rate at which the creditor isn't losing money is more like 33% (presuming business tax rate, or higher for individuals) of 3-4% (for 25 year loans), or about 1-1.3%.

Also, 100% + 0.01%^25 is still more than the sum loaned. And realistically, the interest rate must be higher than 0.01% annually. Sure, you could invest it over 25 years and theoretically beat the interest floor, but this adds a lot of unnecessary risk. When you've already won the game, I think paying the 25% in tax for a guaranteed cash return is worth it over dabbling in high risk, gray area legality tax avoidance.