Are Armand's actions justified?
Armand's actions led directly to the death of Desiree and the baby, but it might argued that the racial climate of the time forced his hand. The historical circumstances made his position/choice extremely difficult. How is it possible to condemn his actions based on this argument?
It is certainly possible to condemn Armand's actions (expelling his wife and child from the home). First, the manner in which he expels Desiree is uncalled for. Even if one justifies Armand's actual choice, he could have asked his wife to leave and sent provisions with her.
More significantly, Armand possesses proof from his mother's letter that a relationship with Desiree (even if she were the one with "tainted" blood) is possible. While it might not be the most convenient situation for Armand or Desiree, he could have sent Desiree to live in Paris or some other forward-thinking area and could have kept up their relationship just as his father had done before him.
By blaming Armand's choice on the racial climate of the day, one assumes that it is impossible for someone to stand up for justice or what is right in such an environment. It's simply not impossible--just difficult.
Whatever the answer is, you have to qualify it in some way. What I mean is that the answer can be yes or no, depending on the perspective from which you consider it.
For instance, if you are speaking in terms of morality, then the answer has to be no. There is no way you can justify throwing out your wife and child just because there is a possibility that they are not "pure-blooded" white. He may as well have put a label on them, calling them unworthy or impostors. No one in their circle would accept them anymore.
And that's exactly why, from a practical perspective, you can say that what Armand did can be justified. He saved his own reputation by casting doubt on Desiree. His friends and neighbors, the whole social system, would shun him the way he shunned her if they even suspected that he was the one who had a black relative. It's convenient that Desiree was discovered abandoned as a toddler. Her background is a mystery, so no matter how white she may appear, doubt can easily be cast on her because no one knows where she came from or who her family is. Why was she abandoned in the first place, hmmm?
As unappealing as his actions are, he really had no other choice. Rather than an outcast, he will be seen as the poor victim!