Could you elaborate please? Not looking for a debate, just want to understand what you mean by "entirely regressive".
One you exchange the money - where an advantage can be gained - then it can be considered a sale and thus taxed. A sale does not necessarily need to be towards consumption.
But, if such a system was in place, the money would be taxed during the purchase of the investment vehicle. A sale is a sale. Unless the money is literally stuck in a mattress, it is going to be taxed upon doing anything useful with it. If it is simply stuck in a mattress for all of eternity, one is really no further ahead. Money only has value when you can use it to facilitate a sale; and when there is a sale there would be a tax.