With $150 billion dollars he could have done a lot more than "argue for" changing taxation. If he had spent that money actively fighting for a better system, maybe that'd be worth something. To sit back on your billions and say "aw shucks, this really shouldn't be possible" is not much of an effort.
Edit: Some people seem to be misunderstanding me. I'm saying if he thought taxation was unequal or thought wealth inequality was a problem, he could have used his wealth specifically to fight against billionaires like himself, not just give money towards generic charitable causes.
Edit: Some people seem to be misunderstanding me. I'm saying if he thought taxation was unequal or thought wealth inequality was a problem, he could have used his wealth specifically to fight against billionaires like himself, not just give money towards generic charitable causes.