When a poem begins with a speaker declaring "now I'm nothing," you know you're in for a heapin' helpin' of some good ol' dissatisfaction. In fact, reading this poem is a lot like listening to that Rolling Stones record. Let's face it, wherever the speaker looks—including in the mirror—he sees things that he wants to change. He's just not satisfied with the status quo. His desire to change his country is really what propels "America." In that way, then, being dissatisfied can be a good thing, since it allows Ginsberg's speaker to make a push for a better world.
The most important quality of the speaker's personality is his dissatisfaction with the status quo. That trumps everything, including his communist sympathies.
The speaker is asking for the impossible. America will never be able to satisfy his demands to be "angelic."