Further, its also discriminatory against people with families, or other hobbies, or against people who don't want to do the same thing that they did 40-50 hours during the week on the weekends too.
I'm not saying that parenting isn't time consuming but it's not as good an excuse when it's so obvious that your lack of time for more programming is also caused by much less noble activities than parenting.
Of course people are going to watch some TV with their families, or play an hour of games to unwind a little, or go watch some sports game with their buddies, or spend god knows how many hours practicing their musical instruments. This is what keeps people sane, productive, balanced, and happy.
Having other hobbies after work is generally a good sign that the person is mature, and has good perspective on life.