>why a wealth tax is needed the whole "buy, borrow, die" thing [...]

see: https://news.ycombinator.com/item?id=48239802

Moreover if the bug is that income isn't tax at death, why not just fix that bug? Otherwise it's like arguing: "wow there are people in poverty? Better have a communist revolution to fix that!"

This is exactly the reason -- or a tax against borrowing against assets once your net worth is high enough -- or not reseting capital gains at death. The entire system is currently basically rigged such that these ultra rich people pay no taxes.