The whole theory of the income tax is that those best able to pay it, pay it. It sounds halfway sensible until one starts to reckon with human notions of justice (”to each his own”) and the disruptive implications of upsetting those notions by government edict. A nation, half of whose citizens don’t pay income taxes, is in a bad position to say fewer and fewer should toil for the support of more and more.
It seems that the income tax is related to distributive justice, rather than commutative justice. But does the Federal tax code pay sufficient attention to the differences in the standard of living that exist between states? Do deductions sufficiently allow for middle- and lower-class families to take care of necessary expenses? (In general, should an income tax be levied on what is truly surplus, rather than what is reckoned by the Federal government to be net income?)
On a related note:
Social Security and Medicare Funding Issues: Even Worse when One Considers Resource Constraints
When we think about the taxes and the federal deficit, we don't usually think of Social Security and Medicare, because in government lingo, the payments we make for these programs aren't taxes, they are contributions, and the funding deficit for these programs is not taken into account in determining the federal deficit.