Confession time. I struggle with the non-dualistic take on Christianity.
Some of my issues are logical. For example, here's a joke I made up.
There are two kinds of thinking in the world.(Do you get it? Any mention of "non-dualistic" thinking creates a dualism.)
Dualistic thinking and Non-dualistic thinking.
I also find the talk of the "true self" versus the "false self" in non-dualistic circles to be, well, sort of dualistic.
To be clear, these are superficial critiques, and the best of the contemplative tradition is not so easily criticized. But pop-contemplative theology is often superficial and dualistic in just these ways.
That said, my deepest reservation about non-dualistic theology is that it clashes with the apocalyptic theology of the New Testament.
As scholars will tell you, both Jesus and Paul where apocalyptic thinkers. And an apocalyptic worldview is rooted in dualisms, the "apocalyptic antinomies": Christ/Adam, Old Creation/New Creation, Light/Dark, Old Age/Age to Come, Death/Life, Christ/Anti-Christ, Spirit/Flesh, Grace/Law.
More, the apocalyptic worldview is rooted in a vision of struggle and warfare between these dualisms, the Christus Victor themes of God liberating us from the dark, enslaving forces of Sin, Death and the Devil.
All that to say, I struggle with non-dualistic theology because my theology has been so shaped by the apocalyptic imagination of the New Testament. I work really hard to see the world the way Jesus saw the world, and Jesus parsed the world with apocalyptic dualisms. Jesus saw himself as casting out Satan, the prince of this world. Jesus preached a message of repentance, not contemplation. Jesus threatened and warned. His vision of the kingdom of God was framed by two apocalyptic destinations, a festive wedding banquet versus the outer darkness where there is weeping and gnashing of teeth. Broad is the way, Jesus taught in the Sermon on the Mount, that leads to destruction.
This is, by the way, why I've become so taken with the work of Flannery O'Connor. As a progressive Christian I'm always tempted to turn Jesus into a non-dualistic contemplative guru of tolerance. Flannery O'Connor helps keep the apocalyptic Jesus of the gospels ever in front of me--the disturbing, strange, unsettling Jesus. The stinking, bleeding, mad shadow of Jesus.
In short, I suspect that a lot of Christians espousing non-dualistic thinking would have a hard time enjoying a conversation with Jesus. To say nothing of Paul, the prophets, or John the Baptist.