The accusation of Polytheism comes from ideas that The Father is not Jesus is not the Holy Spirit and that these are three different beings (which is the view of the Mormons, who still use the word "Godhead" but don't actually really mean it in the same way, and literally mean three separate individuals with separate minds).
The separate minds idea is enhanced by how The Son doesn't know what the Father Knows such as when the Day of Judgment will be, so why if they are one and the same being are they not knowing the same things and having the same one mind?
Furthermore, the question arises as to why the convoluted and confusing façade? Why does God get called Father, and is also called The Only Begotten Son, when in our experience in this world, the word Father and Son do not refer to one and the same person who is their own Son, in fact it sounds absurd and crazy to say someone's Father is their own Son as well, and was born through a Woman themselves. No one says such a thing generally, there is no precedent for such a notion at all, so this is why it sounds mad. A Father is not his own Son in any case other than this supposedly.
Also, a distinction is made between the Holy Spirit and the other two, even though they are all considered God, but if they are the same person, why aren't they simply considered the same and doing the same and knowing the same, and why are they called these confusing things like Father and Son of the Father and Spirit? It isn't as simple as "these are just three forms of One Being", since they are talking to each other, praying to each other, and it doesn't even really appear true entirely that the Son is the Father which is understood to be the main term for God overall.
So instead of this idea, which seemed to develop over time and did not really have much of an earlier precedent (it is not comparable to other Trinities), why not opt for something clearer, more simple, with precedent, easy to understand? Why should one take something as confusing as this:
God is Three Parts, called Father, Son, Holy Spirit, and these are One God, but also Three, and The Father is in Heaven while as Jesus God was on Earth, and God can be in two places at once, as well as anywhere and everywhere (but not in all people, as he was only in Jesus specifically or as Jesus specifically), anyway, Jesus was the Only Begotten Son of God, born through the Virgin Mary by miraculous conception and development in her womb, and so God was born through her as The Son of God, Jesus Christ, Son of The Father, even though he is God as is the Father, but anyway, then Jesus died, but is present in the world still as The Holy Spirit which can be inside people or their hearts all over the world or move them, but is not everywhere or in everyone maybe.
Like, it would make me want to say "please, shut it", its terrible, its a terrible "mystery", and so much simpler to just say There is One God, Jesus is Not God or the Son of God, God is not a Man and doesn't have Sons and is no ones Father, and God is always present everywhere whatsoever and aware of everything, so call upon the One God, not Three or a Trinity.
