In order for this guys argument to hold water he should have used a case other than height which involved a component of personal choice and invoked the same feeling of injustice in people.
Hmm. No one chooses their parents. Should rich kids be taxed like poor kids?
> Would you agree that taxes should be just?
I'll agree that "just" has no agreed-on definition and is used as a way to imply that the other person is bad. As such, I find it a useful signalling device in a discussion.
Are you certain that you don't want to argue that "just", the word on which your argument and position depends, actually has a useful and good meaning?
Because of that I think that the comparison of using height as a deciding factor in taxation is like comparing apples and oranges.
And the math is foolish to begin with: if height determines income level, and you really want to try to equalize for that factor, you should be applying credits/penalties to bring people of different height to the same level -- not taking people who are already at the same level and elevating the short one above the tall one. After all, if they make the same income despite their height difference, it stands to reason that the shorter person is more productive. Applying a credit/penalty when incomes are already equal is the wrong way to argue the (already misguided) point.