>>132798663I always reasoned that the entire reason Meltzer was down in Rapture was because he wanted to save his daughter. By the time Lamb has him, he either dies and faces leaving her daughter that way, or being turned into a Big Daddy to protect her. I think that ultimately, even if it meant the end of his life, he would have preferred her being cured and having a life.
If you notice, the Little Sister with Meltzer also wears a clean red dress, unlike the others.
They also intentioned for Meltzer to know of Delta, and see him as a kindred spirit, facing Lamb and looking for his daughter. However, it got too complicated and they wound up taking it out.