The best argument is that policy like this has nothing to do with what individuals deserve. The idea is that people got rich in part due to all the nice infrastructure we have, and so we could tax some of the income they made off that infrastructure to pay for it all. This includes everything from bridges and buses to food stamps and free clinics - all the things that helped make getting rich possible.
Anyway I'm an anarchist and I would rather have workers in control of the means of production so no individuals get to take all the profits from collective endeavors for themselves, but if we're going to have a state that taxes folks, the argument above is the one I think is best.
Also others mentioned this but hitting the 55% tax rate at $250k means every dollar over $250k is taxed at 55%, but it does not mean that person pays 55% of their income as tax.