The argument is about whether Iris should know the truth or not. Eddie says yes. Joe says no. Eddie asks when does the role in Iris's life outweigh her fathers. Joe says when he marries her. The fact that Joe thinks that A) Being her father gives him the right to keep secrets from her and thus doesn't give the boyfriend the right of telling her , and B) Thinks that once Eddie marries her has can outweigh her Father's judgment and role, and C) Think that their role gives them any right to determine what Iris knows or not , is sexist. It assumes both men in one way or another whether they are her boyfriend, husband or father have the right to determine what she knows because of the role they serve in her life. By implication , if Eddie is her husband, he has the right to tell her the truth and determine what she does and doesn't know. I don't see where that's not the case given what Joe said, regardless of what motivations the writers intended to get across in the scene. Iris can flash a smile, call him daddy , or call him Joe. That really doesn't matter and its not enough to justify Joe's attitude. She's being lied to and she knows it. Joe being her father and having the right to keep it from her because Eddie is not her husband doesn't make it. It doesn't matter if Joe's got this. She doesn't know it because she's being lied to, that's the point.