Incorrect. Slavery was a contentious issue during the founding of the US and for nearly a hundred years thereafter. The Constitution itself contains language (the 3/5 clause) to balance the power of Slave and Free States as a compromise to keep the newly formed country whole. It was no longer considered "normal" outside of the Slave States and the "principled belief" was a result of generations of rationalization and justification, not any true, long-term belief system.
The comparison between slavery in the US at the founding of the Republic and patriarchy is simply invalid. The mere type of slavery practiced by European colonies during that period was an historical aberration, while patriarchy has been widespread throughout history for very valid reasons.