IANAL and this isn't the legal justification. But US corporations are treated with rights similar to actual people with slightly better treatment in some ways,

IANAL and this isn't the legal justification. But US corporations are treated with rights similar to actual people with slightly better treatment in some ways, slightly worse in others. So: morally corporations should pay income tax because all persons are subject to income tax. And we have decided that corporations are persons. It's no more a "bonus" tax than it is a bonus tax when I pay my accountant and she also has to pay tax on that income (even though I have already paid tax on the money).