My answer to that is that the stupid will fall for anything. God the Father, Jesus the Son and the Holy Spirit all exist together. If the stupid cannot believe this, then I cannot stop them, just like I cannot stop the Democrats from being the evil, blind liberals that they are.
Since the night Obama won the election I pretty much worry only about the family members that sit at my kitchen table, because those are the mouths I have to feed and the ones I can pray for. I’m their mother. I have to shut out the rest, for my own sanity a lot of the time.
IIRC, some Muslims believe Christians are polytheistic, because of the Trinity. I may be wrong though.