As I shared on the Trinity earlier
here, its but a relational construct, a model of 3 Gods within a compound unity, a concept of a Godhead with 3 persons. It might be more, but I treat it as just that in my former commentary. There are links to the 'Paradise Trinity' too, for a greater more wondrous cosmic conception of the Godhead found in the Urantia Papers. Again, I mainly treat this in the last commentary as a CONCEPT.
A purely monothetist Unitarian Christology is a simple rational view to take, and is the view of orthodox Jews and the most early christians. Trinity creeds, conceptions were formulated centuries later, but any student of history and theology worth their salt knows these things. I agree with the quote above, to a certain degree. I can tolerate a traditional-orthodox concept of the Trinity as
one 'god-concept' among many others, its only when some push it as
absolute truth,
dogmatically, and furthermore condemn Unitarians or demonize them for not accepting that 'concept', and being mean, cruel, demeaning and the like that is just ridiculous and unnecessary. The folly is amplified when some creeds claim that any not accepting the terms of
their creed CANNOT BE SAVED. -

(enter Athanasius, at least the creed credited to him, questionable to some).
Uh huh.
Again,...and I'll say it with heaven as my witness,....
I have yet to see any advantage of believing the traditional-orthodox concept of the Trinity over a historical biblical Unitarian view of Jesus, as the Messiah-Son of God. I find other views, among spiritualists, Gnostics, mystics of various schools, etc. as having just as good a view and respect for Jesus. What counts according to the master is having a 'pure heart'...for these are they who will SEE 'God'....among other essentials required for entering the kingdom. A belief in the Trinity is more or less inconsequential.
If it can be shown that much war, cruelty, human suffering and pain can be associated with a Trinitarian belief, within whatever time period of Christiainity remains to be supported, but it seems that its was during the doctrinal development and formalizing of certain doctrines...that wars, cruelty and intolerance was rampant. I dont know what William Penn is referring to in particular, if an inference could be made.