Moloch in whom I sit lonely! Moloch in whom I dream Angels! Crazy in Moloch! Cocksucker in Moloch! Lacklove and manless in Moloch!
This line takes us "inside" the insane mind, where we find the speaker "lonely" but also dreaming, insane but sexually active.
"Manless" could mean "without manhood" or "without a man to love."
Moloch who entered my soul early! Moloch in whom I am a consciousness without a body! Moloch who frightened me out of my natural ecstasy! Moloch whom I abandon! Wake up in Moloch! Light streaming out of the sky!
The speaker can't seem to decide exactly what Moloch is, but he knows it has been with him since a young age, or "entered [his] soul early."
It is opposed to both nature and the body, and though the speaker "abandons" it, he still "wakes up in Moloch."
In this long list of names (look how many exclamation marks!), Moloch is equated with: war, capitalism, nationalism, government, and hostility to sex.
They broke their backs lifting Moloch to Heaven! Pavements, trees, radios, tons! lifting the city to Heaven which exists and is everywhere about us!
"They" are the people who built the neighborhoods and cities of America: the American workers and those "best minds."
They installed the pavements and planted the trees. People thought that we could lift Moloch and the city to Heaven, but they didn't realize that Heaven is already "everywhere about us."
They were looking in the wrong place for the divine. They thought it could be found in "stuff" (or material objects), when in fact it exists in people.
Visions! omens! hallucinations! miracles! ecstasies! gone down the American river!
Ginsberg was a "visionary" poet, but he believed that American capitalism and modern-life had destroyed the ability for people to have visions.
So the omens, hallucinations, etc., are not part of Moloch. They are good things. But they have been destroyed by Moloch. They have "gone down the American river," which means they were treated like pollution or like some shipment of cheap goods destined for a faraway country.