Quote by Justice Clarence Thomas in the Marriage Equality Decision by the Supreme Court

Can anyone understand what Justice Clarence Thomas meant by the following quotation which is from his dissenting opinion in the case of Obergefell v. Hodges, decided June 26, 2015, at page page 17:

“Slaves did not lose their dignity (any more than they lost their humanity) because the government allowed them to be enslaved.”

"Slaves did not lose their dignity"? They didn't lose their humanity?