If you act in a certain way, you are free to accomplish that for yourself. Only ever do a same-day exercise-and-sell. Never exercise early. Never exercise-and-hold. Enter into a 10b5-1 that ensures you sell any shares immediately upon vesting. I think that covers all the cases and you're protected against being taxed on paper-only valuations.

That doesn't mean that your preference should preclude other people from acting differently.

This opens a number of loopholes related mostly to income and estate tax avoidance. Shares of companies can be transferred to heirs for an arbitrary strike price and if they're never sold, there's no capital gain tax, no income tax and no estate tax liability generated. Rinse and repeat for multiple generations.

AMT is a quick fix to allow the government to tax the transfer of assets per se.