Sounds as if Rader is a psychopath, and people like that can compartmentalize their lives surprisingly well. They manage a normal work existence and confine their nuttiness to off hours or whatever is the focus when they're 'correcting' things, so those who know them superficially think they're normal.
Not that my former next door neighbor was a psychopath, certainly not...but he was a control freak. He and his wife had five children, boys and girls -- teenagers. One summer his wife mentioned they were driving to Canada, where they intended to go camping for a few weeks. This trip was to take five hours. I laughed and said how would they manage to stay sane, five hours in a station wagon with five teenagers? I stopped laughing when she said that was no problem. The kids would sit silently for the entire trip since they were all terrified of their father. She was dead serious, but didn't divorce him until all the kids were grown and out of college and she'd retired from teaching with a pension large enough to make it on her own.
"Sounds as if Rader is a psychopath,"
I always figured whoever BTK was, he was more than likely either mentally very crazy, or there was a very specific reason for his crimes. I still do not know which it is.