There are many infuriating things about the current federal tax rules, but the one that I find the most egregiously unfair and potentially damaging to the economy is the situation with deductability of interest.

In 1986, individuals were no longer allowed to deduct loan interest, except in special cases, and for their home mortgages. The arguments for this change were simplification, discouraging installment borrowing and more revenue for the government. The only valid argument is the first one, since it's not clear that discouraging installment borrowing is a good thing for either the economy or the individual.

But it did indeed simplify taxes--there's no longer any need to find all of your interest deductions, and add them up, since they're no longer relevant to your return. Of course, in exchange for this "simplification," most people pay much more in taxes than they did prior to the change. This has resulted in the growth of "mortgage lines of credit" since now the only way to make the interest deductable is to borrow money against your house.

This change was outrageously unfair, because they now get you coming and going. You still have to pay tax on interest earned, but you're not allowed to deduct interest paid. So interest counts only when it's incoming--not when it's an outgoing expense, unless it's going into some other investment (not consumption). (Thanks to Carey Gage for pointing out my previous erroneous statement, now down the memory hole).

But the situation has a more problematic effect (speaking personally)--it discourages small business formation. Suppose someone has an idea for a business startup, but limited access to capital. Well, one way to do it, if one has a good credit rating, is to do "venture capital by Visa." Borrow the money from your credit card, and pay it and the interest back from the proceeds of the venture.

Now most financial advisors would say that this is insane. Of course, those same financial advisors would probably also say that starting your own business is insane as well, given the rate of failure of startups. So given that you're going to be an entrepreneur anyway, it's not that much nuttier to borrow the money to do it from Mastercard, instead of Aunt Nellie.

And therein lies the problem. Clearly, the interest that you're paying on the loan is a business expense. But if the main thing that you need the money for is to cover your personal bills (rent or mortgage, groceries, gas, etc.) while you're getting the business going, there's no way to deduct it under the current rules.

Well, wait--there is one way. You can borrow the money, then relend it to the business startup, and then pay yourself a salary from the loan. This allows you to deduct the interest for the loan to your business. But there's a big problem--it also means that you have to pay federal income taxes on it, including FICA, and possibly even things like unemployment insurance, because it's now taxable income to you.

So that's the choice you have. You can simply borrow money to support yourself, but you can't deduct the interest because it's not considered an allowable business expense, though clearly it should be. Or you can borrow the money and lend it, in which case Sam takes a huge percentage off the top before you can get it to pay your bills.

Either way, I suspect that there are a lot of businesses (including space businesses) that don't get started because of this financial catch-22, which could be eliminated by simply returning fairness to the tax system, by either excluding interest income from taxes, or restoring the interest deduction.