Let's not pretend though that there is some kind of historical justification here. It seems foolish to try to argue that Helen of Troy could possibly have been black in this fictional story. It's fiction and these are modern actors. Just say what you want and throw the justification away as it is stupid. Offering some sort of historic justification here is as much of a stretch as trying to claim Jesus was potentially a blue eyed white guy.
I think Lupita Nyong'o is a phenomenal, Oscar-winning actress, and I have zero issue watching her play Helen of Troy because theater relies on talent and imagination, not DNA. My issue is with the hypocrisy of the discourse. When people try to invent fake historical justifications like using ancient slavery to claim Helen could have been Black it is just as dishonest and wrong as Europeans pretending Jesus was a blue-eyed white man. Let's stop rewriting actual history to justify modern creative casting. Just admit it's a creative choice in a fictional adaptation and move on.
Why would I continue reading lies? What's the benefit for me? You guys act like you didn't spread Gay fanfiction about Ancient Greece for decades. Clowns.