They were people of their time and place, and what they were taught to believe did not seem wrong to them. I would like to believe that I would not have gone along with the crowd, but I cannot honestly say I would have had I been raised to believe that what they did was acceptable.
Never the less, they joined the Union with the premise that their peculiar institution would continue, and this position represents their free will choice on the matter. What the Federals did to force passage of the 13th and 14th amendment does not.
Wrong.
Passage of the 13th (1865), 14th (1868) & 15th (1870) amendments represented the free-will choice of a majority of voters in those states at that time, and those choices have never since then been repealed.
Of course, for some years after the Civil War voting franchise was restricted to those who had not participated in the rebellion.
The original 27 ratifying states included nine Southern:
Nine other states did not ratify the 13th at the time, but all have since ratified, the last being Mississippi, certified in 2013.