Irwin argued in court that the Sixteenth Amendment of the U.S. constitution did not apply to him. While many people might argue this amendment was never properly ratified, silent acquiescence is a form of consent. Today, if you receive a summons to appear in court and you do not appear after receiving proper notification, what happens? The court could enter default against you for your failure to respond and that quickly becomes your problem. That would mean the Sixteenth Amendment did legally pass by the consent of the majority of the states, as no response objecting to the proposed amendment was ever received or objections were not received in time.
"No private person has a right to complain by suit in court on the ground of breach of the United States constitution; for, though the constitution is a compact, he is not a party to it."