A practical problem of wealth accumulation is that it eventually becomes a moral hazard. If you have people with more $10B and a system of unlimited political contributions as in the US, they have so much power that it is difficult to maintain the democratic equilibrium. It is now known that the Koch brothers and Sheldon Adelson have more power over the republicans than the RNC, having elected hundreds of local and national politicians. In the left there is George Soros and a few others. Are we really willing as a society to give away so much political power to billionaires? I think a very practical solution is an extreme large tax on billionaires. There is no reasonable reason why a single person would like to have more than a billion dollars. This is practically an inexhaustible amount of money that should be considered as a practical limit. After that, you can happily pay 99% tax and enjoy making this country better.