Slavery paints itself again in its complete abrogation of marriage, recognized as a sacrament by the Church, and recognized as a contract wherever civilization prevails. Under the law of Slavery no such sacrament is respected, and no such contract can exist. The ties that may be formed between slaves are all subject to the selfish interests or more selfish lost of the master, whose license knows no check. Natural affections which have come together are rudely torn asunder; nor is this all. Stripped of every defence, the chastity of a whole race is exposed to violence, while the result is recorded in the telltale faces of the children, glowing with their master's blood, but doomed for their mother's skin to Slavery, through all descending generations. The Senator from Mississippi [Mr. BROWN] is galled by the comparison between Slavery and Polygamy, and winces. I hail this sensibility as the sign of virtue. Let him reflect, and he will confess that there are many disgusting elements in Slavery which are not present in Polygamy, while the single disgusting element of Polygamy is more than present in Slavery. By the license of Polygamy one man may have many wives, all bound to him by the marriage tie, and in other respects protected by law. By the license of Slavery, a whole race is delivered over to prostitution and concubinage, without the protection of any law.And that was an accurate, reasonable description of the reality of slavery in the US.
The New York Times has the text of the speech online. I rely here on the text from the version published in 1863 as Barbarism of Slavery.
[This post has been updated for clarity.]