Dr. Ben Carson on Monday offered an alternative interpretation of forcibly bringing 12 million African slaves to the Americas between 1526 to 1867, comparing them to immigrants — who voluntarily chose to come to the United States — during his first speech as secretary of Housing and Urban Development (HUD).

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Extolling the virtues of the United States' "can-do society," Carson said there were "immigrants who came here in the bottom of slave ships, worked even longer, even harder for less."

Despite being enslaved, "they too had a dream that one day their sons, daughters, grandsons, granddaughters, great grandsons, great granddaughters might pursue prosperity and happiness in this land," Carson said.

The speech also touched on the unlimited capacity of the human brain, but it was Carson's comments on slavery that grabbed the headlines and garnered widespread criticism online.

This isn't the first time a comparison between slavery and immigration has caused controversy. In 2015, textbook maker McGraw-Hill came under fire for including information and graphics about the Atlantic Slave Trade in a section on "Patterns of Immigration" in the U.S., The Washington Post reported.

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McGraw-Hill apologized for the mistake, pledging to "do better" and "update this caption to describe the arrival of African slaves in the U.S. as a forced migration and emphasize that their work was done as slave labor."

Neither Carson nor the White House have issued further comments on the matter. Neither immediately responded to ATTN:'s requests for comment.