Out of interest what are the positives? Other than cultural, in flagrant displays of excess, I can't think of anything they couldn't accomplish by them existing as poorer business leaders and having competent national wealth funds empowered to lend/give grants.

What I'm saying is you may be defending billionaires when you mean to be defending a system you believe is optimal but still has the negative outcome of billionaires (not to imply the billionaires themselves are intrinsically bad as people but the concentration of wealth in their hands is).