>No single human needs a billion dollars

And no human being needs however much you're earning, as people in third world countries survive on far less. Life's about more than "need", and if you give the government enough power to prevent people having more than they need, you inevitably create a horrible dystopia, probably accompanied by genocide, like happened in Russia, Chinaa and Cambodia when they let the government make the final decision on how much wealth people are allowed to have. Because when the people in the government have that power, they'll inevitably decide that they're the only ones who should have wealth.