for starters, you only pay on 50% of the gain, since capital gains are favoured form of wealth.
Since I don't think you are trying to argue that you should pay tax on 100% of the gain, you're not suggesting they shouldn't be taxed at all?
Or perhaps you would have preferred to pay every year over the past 20 years?....even though you didn't have the cash in hand...rather than have it deferred until you sold it and realized the cash.
Or do you have another alternative?