This part I also found hardest to interpret. I would say, the general symbolism is hard-headedness. An uphill battle against flatheaded armless Hammer-Heads. They fly over them. Something to be avoided/bypassed. Could be more in there. Some references to US history perhaps?

The commie stuff is the Red Poppy Fields that brings them to sleep before they first visit Emerald City.

Definitely read the original. It's a relative quick read.

Audiobook: https://www.youtube.com/watch?v=F03Up9ZXbJs