No it doesn't say that. It says that the tax is imposed upon all who have "taxable income" and who are required to file a return. Section 1 implies no liability whatsoever. It is specifically limited to those who file returns.
Two questions. For purposes of section 1, where is "taxable income" defined ? Where does section one put limits of only taxing someone required to file a return. The only occurance of the word "file" in section 1 is in under (g)7 and is only relevant to a child being required to file a return.
Section 1 implies no liability whatsoever. It is specifically limited to those who file returns.
I read "Imposes a tax" as equivalent to liable. So do the judges. However, technically speaking a person is not liable until a tax is assessed.