Wow. You don't see how including all things that affect net position as being part of determining net position?
But at my point in life I've acquired lots of after tax assets. If our tax system is changed to a sales tax system, I will not be able to buy as much stuff with those assets - I say that is not fair at all - it is theft of my property. Acknowledge and compensate me for that reduction in value, I might be able to move on to support this kind of gross change in the way we fund government.
I would suggest easing into such a change, because the dislocations and personal rearrangements that would result from an instant gross change of this sort would send violent shock waves through our economy.