Earlier quoted context omitted.
It’s fair because otherwise you could compensate people for zero tax. For example, you have a CEO that can either be paid: 1) $1m in cash 2) $1m in stock 3) an option grant to buy 1m shares at $0.000001. Each share has a FMV of $1. Without AMT, you could always take (3) and they would get $1m of stock for $1. Tax free.
With (3), they'd be taxed on the gains when they sell. Not "tax free" at all. The difference is that they wouldn't be taxed until the gains were realized not when they were imagined on paper.
That gap between strike price and FMV is much more like compensation than it is an investment.