I don't want to put words in your mouth, CynicalBear, so please clarify something for me. Are you saying that the text is fairly straightforward about the One causing people to fall for the deluding influence is God? If so, then you and I are in agreement. That is precisely what the text is getting at. And it is at least a strong possibility that this is why all of the nutcase cults are running around claiming all sorts of goofy things, as the OP said.
But, the fact that God manages all of the beings in this universe, including the wicked waywardness of Satan and idiotic people claiming to be "Christians", is often considered almost heretical by those who do not know the Scriptures. But, God is in fact, God. And everything is subject to His unlimited sovereignty (even when the text says by means of the Holy Spirit. The Spirit, after all, is part of the Godhead.).
Rashputin may be right about Rome denying this. If he is, such a position is outlandish in the face of the text, itself. It would, however, then be just one more error Rome has promulgated.
Yep, looks like we agree Dutchboy88.