The vast difference between "becoming God" (Christian theosis) and "becoming a god" (that other religion) is entirely lost on some folks.
It's(they're?) God's wrath on our lousy teaching. E.G. Jehovah's Witnesses arose because we weren't doing a good job on Eschatology and the "personal" (for want of a better word) nature of God. So here comes a group which has two things to say: "God has a name, and the end is coming."
We do a bad job on the sanctity of the family and on theosis, and we get Mormons.
Sorta like that.
To me it shows that we really are built for God, and if we don't get the real deal we grope around for something kinda like Him and his Truth. While not in any way wanting to minimize the awfulness of lousy ecclesiology and so forth, and while also conceding eagerly that Protestant group (B) usually arises in response to the deficiencies of Protestant group (A), we also need to consider that our deficiencies in teaching and living help provide fertilizer for these noxious weeds -- and their nature and qualities can help us diagnose our errors.
At least, it's a conjecture of mine.