Sorry, perhaps I missed something -- I assumed there are Monists who have this belief system, which would be a movement/group/religion. I could just be making too big an assumption
I have met others who understand my beliefs and even believe in some of them themselves. Yet, we are not all the same.
The Taoists I have spoken to understand such things, but view it in a different manner. I have spoken to Hindus and Buddhists who also understand such things, but there are many sects of such religions.
To say that Monism is an "organized religion" would be wrong, I think. To say it is a group is mis-leading, as there are many monistic thinking people of different views. To say it is a movement, I'd have to disagree. I met very few who even have monistic tendancies, and those who do subscribe to a branch of what is viewed as a religion.
To go back to your comments Cloaked:
It's certainly, to an extent, a biblical concept. God created everything, so nothing is good or evil on its own -- all things serve the will of God, who is in everything. The duality is an imposition created by people, but it has nothing to do with the true nature of the universe.
Such concepts are older than the Bible and those who follow the Biblical religions seem to have little understanding of such a concept (in my opinion). There would be a difference in what you that "nothing is good or evil on its own" and saying there is no good nor evil. (Also, if God created good and evil; then is a construct of people?) There is also a difference in saying "God, who is IN everything", God is everything, God is all things, and God does not exist.
Where I differ from a Taoist and others is to say that: God is all as one as nothing. Many other ways seem to lose the "void" concept which is why I cannot subscribe to such a way of thought. Though many of such ways tend to understand me more and I them, we do differ in some aspects.... as Christians of different denominations differ, or a Methodist to a Catholic, etc...
Monism is really in these days more of a theological concept, not any type of organized religion.... hope that maybe cleared up something.