The way Lex treats women in Batman v Superman: Dawn of Justice always stuck out to me. In my opinion, Lex carries a sick philosophy about the female characters throughout this film. This carries across the women he hates and those that hold a special place in his twisted worldview.
Lex seems to love women yet hate them as well. I’d like to think this love/hate complex started from Lex’s own mother, who presumably died or didn’t do anything to protect him from his father’s abuse when he was a child. This leads him to look down on women and think women are generally weak and manipulatable. In his own word, they have “little minds”.
He does not reject all women though, as he seems to have an intimate relationship with Mercy throughout the film. That smile Mercy gives him when he says “Emerald City…Beautiful”, is perhaps indicating that she thinks he is complimenting her. That hints at their involvement to a certain extent. Apart from the metaphorical “Lex lost his mercy”, I think Lex had another reason to end her life.
That reason, I feel, is that he doesn’t want to have any weaknesses. He may consider every man’s “special lady” (whether it was a mother or a lover) as a fatal weakness. He sees weakness through Superman and took this as his leverage to force “The greatest gladiator match.” Lex specifically kills Mercy before he confronts Superman on the roof of Lex Corp’s building, to keep himself safe from the exact flaw he is exploiting in Superman. This is why he kills the last person he might actually care about, and he defeats Superman with that “flawless” disposition which made him more confident than ever.
Lex looks at this alien, who seems all powerful, gets emotionally attached to two powerless “Witch-like” women. Lex believes he is superior, despite having no power like Superman. He believed he won the moment he feels the sense of control back in his hands. In this case, he doesn’t need his helpless/long dead mother to save him anymore.
What Zack Snyder explicitly shows though, is Lex is wrong about women and has been proven in the wrong about women in BVS multiple times.
It starts with the semi-mother figure for him in Senator Finch. Whichever part of her that reminds him of his own mother was not important (it may be something as simple as same age or same hair color); the important thing is that he did not treat her condescendingly like he how he treats other women. He even seemed to be drawn to her. The moment she finds out Lex is trying to manipulate her too, she exposed it right in front of him, and Lex can’t take “No” from a woman, not even from his substitute “mother.”
The second moment is when he gets trophy-to-be from Martha’s kidnapping. He tends to enjoy getting a trophy from a conquest, like the Big Neon Sign he took from his dead father. This time he took a timer from Martha’s kitchen (restaurant) and it’s going to countdown his victory.
What he didn’t see was that he was wrong again. All this time he could only see the weakness and helplessness of women, but never saw their strength, brilliance and bravery. He never considered the possibility that a person’s greatest weakness can also be their greatest strength!
Even in the end, Lex did not understand the reason for his failure. but Zack made sure the audience knew. We know Lex lost to his arrogance, and in his underestimation of the women characters like Lois and Martha. On that count, Lex became more “alien” than the one he was trying to destroy.