Wealth concentration of this magnitude seems like an extremely inefficient allocation of capital. Dollars get things done and having them concentrated and controlled in a just a few spots seems like the worst way to apply their value. A person of this level of wealth has no problem using the wealth simply for personal gain.

The concentration of wealth seems to undermine democracy.

Democracy seems to be working out decently well, concentration of wealth seems to run counter to democratic ideals. I guess that's how it has always been in capitalism: undemocractically-selected application of larger amounts of capital.

For instance, if one of these wealthy people decides to spend on a $1BB on PR campaign to run for office and they win; they will have effectively bought the outcome of the election like any other off-the-shelf product.

This level of wealth inequality could be a national security risk.

If the level of wealth concentration gets too high, we could start seeing a new market of privately-owned paramilitary sharing the space with what was originally occupied by branches of the military.