I agree with this guy. A person sells their services to their employer. What's the difference between that and selling real estate. You may say that the person had to buy that property but, quite often, preparation for an occupation requires a good deal of investment as well.
I will agree that a sales tax is an indirect tax but I can't see how the income tax can be an indirect tax. I guess the Congress wasn't real sure either because they included a fix in the sixteenth.
What's the difference between that and selling real estate.
None at all, for "selling" real estate is a activity of commerce the activity of exchange being taxable as an "indirect" tax against property involved in that taxable "exchange". Merely holding ones own property for ones own use is not involved in an event nor an exchange with another, thus is not subject to an indirect tax for lack of an "activity" against which a tax may be levied.
Therein lay the distinction between indirect and direct, commerce is taxable under an indirect tax as it invokes relationship between individuals engaged in a taxable "exchange" or "event". Ownership of property not engaged in an "exchange" or "event" between persons is a direct tax on ownership by one person alone.