In part using the Montana poem as a foundation, in 1941 Siegel proclaimed a new approach to philosophic thought that he called "Aesthetic Realism." Siegel described the philosophy as being based on the premise that “The deepest desire of every person is to like the world on an honest or accurate basis." The statement was certainly admirable, but eventually the movement evolved into an often-inappropriate self-help agenda that became thoroughly cult-like. Today, the Aesthetic Realists are a tiny and eccentric fringe group, probably wondering why the Scientologists are the ones who get all the attention.
But I don't think the whole Aesthetic Realism thing really lessens the literary merit of Siegel's Montana poem. It's too long to fully reproduce here, but here are a few sample lines:
Indians, Indians went through Montana,
Thinking, feeling, trying pleasurably to live.
This land, shone on by the sun now, green, quiet now,
Was under their feet, this time; we live now and it is hundreds
of years after.
Montana, thou art, and I say thou art, as once monks said of God,
And thought, too: Thou art.