Capital gains tax is assessed in fiat currency units. So, through monetary debasement, your assets become more valuable in those units, irrespective of the real market value.
For example, suppose you buy a gold coin for $1000 and sell it later for $2000, over a period where the money supply doubled. You owe tax on the $1000 āgainā, even though some or all of that gain may be attributable to the intervening monetary debasement.
Had there been no debasement, your capital gain may very well have been less, zero, or even a capital loss, for which youād have owed no tax. Capital gains tax, by being assessed in fiat currency units, and not adjusted for monetary debasement, punishes you for the governmentās own money printing.