Is this not an exemplar of the slippery slope fallacy?
no, it's not. It's math. If you make a rule that you lower the person at the top of the pile, over time, there will be nobody left to lower - everybody will be at the top of the pile.
The fact people say 1 billion is too much money, or 1 trillion is too much is something to dig into - the number is relative! 1 billion is only a lot because not many people have a billion dollars. If inflation keeps up, one day everybody will be a billionaire.
How so?
Well, suppose we say, nobody should be a trillionaire - is this an arbitrary number, or is it aimed at the richest person? Clearly, the latter. Now if we carried this out, now there are billionaires remaining. Well, nobody should be a billionaire, one might say. Most will agree. So the wealth of billionaires is taken away, and redistributed evenly.
This will continue, with the majority of people below the average wealth level, demanding a more equal playing field. You can see how it ends