In "Desiree's Baby", why does Armand marry Desiree without considering her origins?

Armand was in love with Desiree. He fell in love with her at first sight, like a pistol shot, the story tells us. 

"Armand Aubigny riding by and seeing her there, had fallen in love with her. That was the way all the Aubignys fell in love, as if struck by a pistol shot. The wonder was that he had not loved her before; for he had known her since his father brought him home from Paris, a boy of eight, after his mother died there. The passion that awoke in him that day, when he saw her at the gate, swept along like an avalanche, or like a prairie fire, or like anything that drives headlong over all obstacles." (Chopin)

Therefore, once he was in love with her, he was consumed with the idea to marry her.  He did not care about her ancestry, or her background.

Because Desiree was adopted, and her biological origins were unknown, it is logical for Armand to assume that the reason the baby bears African ancestry traits is due to her biological family connections. 

Since Desiree's ancestry is not known, they could not rule her out as being part African, even though she does not look African.  There were people who were just 1/4 African who did not look African, but carried the ancestry in their genes.