It's designed to prevent you from being able to defer taxation (interest-free leveraging of income you'd otherwise have paid in tax, essentially) or to reduce y

It's designed to prevent you from being able to defer taxation (interest-free leveraging of income you'd otherwise have paid in tax, essentially) or to reduce your taxation to the long-term capital gains rate. I'm not sure if the authors of the AMT really considered how options with limited liquidity could create this bind.