The problem with the income tax was actually Article 1, Section 9: No Capitation, or other direct, Tax shall be laid, unless in Proportion to the Census or Enu

The problem with the income tax was actually Article 1, Section 9: No Capitation, or other direct, Tax shall be laid, unless in Proportion to the Census or Enumeration herein before directed to be taken. It explicitly bans direct taxes except for a fixed tax per person. A income tax which directly taxes individuals almost certainly constitutes a direct tax by any reasonable interpretation. The 16th amendment directly repudiates that section and grants the explicit power to levy a income tax.