Alex:

I don’t see why you need a Trinity in Unity within the Godhead in order to account for unity and diversity. A muslim could argue from the unity of Allah’s diverse attributes that they can account for unity and diversity.

Necessitarian:

1.) Unitarian Gods lack personal diversity, and so unitarian Gods must resort to explaining the one-and-many relation in impersonal terms. This is to say that, at bottom, unitarianism answers metaphysics the same way Hinduism, Taoism, and monist naturalism do: the one-and-many derive from impersonal facts. Unitarianism reduces to impersonalism.

2.) Concurrently, unitarian Gods cannot even maintain traditional attributes. How can an isolated person possess or instantiate relational love? How can an isolated person know adoration? How can a unitarian God possess worthiness or glorification prior to creation? Worst of all, the unitarian God faces a dilemma.

Unitarian personhood does not reside in the presence of another divine Person. This means the unitarian God is individuated by the abstracted list of divine attributes simpliciter and so his personhood is defined by impersonal laws, bundles, Forms, whatever paganism suits your fancy. In summary, a unitarian God cannot be God because unable to have the supposed diversity of attributes in the first place.

3.) Unitarianism contradicts Scripture.
One could trivially answer my objections in (2). They could resort to egoism with respect to love and say that all love derives from self-centeredness. They could resort to a Cartesian God who isn’t rational at all and so can’t be critiqued. They could borrow from atheistic Platonists and say God’s worthiness is an irreducible fact (i.e. brute fact).
In any case, when you get to the nitty gritty, unitarianism has more in common with Gnostics and Hindus than with Jewish Monotheism.