But the Spirit says expressly that in later times some will fall away from the faith, paying attention to seducing spirits and doctrines of demons,
By "doctrines of demons," Paul has reference not to teaching about demons as MacKnight and Newton believe, but to teachings that are inspired by demons--teachings that come from demons. In their fight against Roman Catholicism, both Newton and MacKnight interpreted this passage as an exclusive reference to Catholicism. While it certainly includes the abuses of that religion, I do not believe it is limited to it, for numerous false religions have espoused these false doctrines (second century Gnosticism as well as numerous modern cults, Seventh Day Adventists among them).