I read the chapter again and I simply can't understand why you people arrived at that conclusion. Maybe your expectation is biased towards tragedy all the time?
I re-read the chapter and is not hard to understand what his father is thinking.
I believe that he just meant for his son to work hard and responsible enough to have the means to sustain both himself and her, because not only he thought that she is not able to contribute much monetarily, but also because she is worth the effort.
She lives with his son, his poor son, in a tiny room with zero luxuries. Despite that she is content because her primary interest is to be together with him. She doesn't study but enjoy learning every day practical things she teaches her. She pays attention to him, she values him and what he does. She expend the little she had to make the house more comfortable for the two of them. His son didn't wanted to talk much about her and her circumstances, but she is honest enough to admit openly bad things that she did.
Think about this yourself, if not for her mental disorder Megumi would be easily considered by anyone as very "decent".
From a father's perspective, he is doing well.