The argument for a higher tax on income above a certain level is that it helps prevent tyranny.
In the US, anyway, wealth equals power. Great wealth accumulated in few hands shifts a great deal of power over the nation from the populace to those hands. Without some constraint, this poses a real threat to overall freedom and liberty.
You say that wealth accumulation poses a (vague, potential, in the future) threat to overall freedom and liberty... but arbitrary wealth redistribution poses an immediate, obvious threat to overall freedom and liberty _right now_.
In the US, anyway, wealth equals power. Great wealth accumulated in few hands shifts a great deal of power over the nation from the populace to those hands. Without some constraint, this poses a real threat to overall freedom and liberty.