There's a sub-forum in CH for speculative theology and world religions. The theology forum is intended for discussion between Christians who accept the Nicene Creed. If one rejects the holy trinity and the incarnation or even if one does not but wishes to discuss non-trinitarian views then world religions and speculative theology is the right place for such discussions. It is not my role to decide who is and who is not in God's grace but it is self evident that a discussion that sets out to teach some view in which the holy Trinity is not accepted is not a Nicene Christian discussion. Nothing mean spirited about it.
The Athanasian Creed explains (more a case of baldly stating) that belief in the Holy Trinity is necessary for salvation.
Whoever wills to be in a state of salvation, before all things it is
necessary that he hold the catholic [apostolic/universal] faith, which
except everyone shall have kept whole and undefiled without doubt he will
perish eternally.
Now the catholic faith is that we worship One God in Trinity and Trinity in
Unity, neither confounding the Persons nor dividing the substance. For
there is one Person of the Father, another of the Son, another of the Holy
Spirit. But the Godhead of the Father, of the Son, and of the Holy Spirit,
is One, the Glory equal, the Majesty coeternal.
Such as the Father is, such is the Son, and such is the Holy Spirit; the
Father uncreated, the Son uncreated, and the Holy Spirit uncreated; the
father infinite, the Son infinite, and the Holy Spirit infinite; the Father
eternal, the Son eternal, and the Holy Spirit eternal. And yet not three
eternals but one eternal, as also not three infinites, nor three uncreated,
but one uncreated, and one infinite. So, likewise, the Father is almighty,
the Son almighty, and the Holy Spirit almighty; and yet not three
almighties but one almighty.
So the Father is God, the Son God, and the Holy Spirit God; and yet not
three Gods but one God. So the Father is Lord, the Son Lord, and the Holy
Spirit Lord; and yet not three Lords but one Lord. For like as we are
compelled by Christian truth to acknowledge every Person by Himself to be
both God and Lord; so are we forbidden by the catholic religion to say,
there be three Gods or three Lords.
The Father is made of none, neither created nor begotten. The Son is of the
Father alone, nod made nor created but begotten. The Holy Spirit is of the
Father and the Son, not made nor created nor begotten but proceeding. So
there is one Father not three Fathers, one Son not three Sons, and Holy
Spirit not three Holy Spirits. And in this Trinity there is nothing before
or after, nothing greater or less, but the whole three Persons are
coeternal together and coequal.
So that in all things, as is aforesaid, the trinity in Unity and the Unity
in Trinity is to be worshipped. He therefore who wills to be in a state of
salvation, let him think thus of the Trinity.
But it is necessary to eternal salvation that he also believe faithfully
the Incarnation of our Lord Jesus Christ. The right faith therefore is that
we believe and confess that our Lord Jesus Christ, the Son of God, is God
and Man.
He is God of the substance of the Father begotten before the worlds, and He
is man of the substance of His mother born in the world; perfect God,
perfect man subsisting of a reasoning soul and human flesh; equal to the
Father as touching His Godhead, inferior to the Father as touching His
Manhood.
Who although He be God and Man yet He is not two but one Christ; one
however not by conversion of the GodHead in the flesh, but by taking of the
Manhood in God; one altogether not by confusion of substance but by unity
of Person. For as the reasoning soul and flesh is one man, so God and Man
is one Christ.
Who suffered for our salvation, descended into hell, rose again from the
dead, ascended into heaven, sits at the right hand of the Father, from
whence He shall come to judge the living and the dead. At whose coming all
men shall rise again with their bodies and shall give account for their own
works. And they that have done good shall go into life eternal, and they
who indeed have done evil into eternal fire.
This is the catholic faith, which except a man shall have believed
faithfully and firmly he cannot be in a state of salvation.