> we could tax something like 5% of stock buybacks and completely rebuild our entire society from the ground up.

In 2018, there were a total of $800 billion of stock buybacks, and this was an utterly exceptional moment when corporations were essentially forced to make them due to tax advantage. So even if your theoretical tax didn't impact buyback behavior at all (it would) and buyback rates returned to 2018 levels (they won't), you would raise $40 billion per year. It would raise federal tax revenue around 1%. How do you envision spending that to completely rebuild society?