I want to hear more about Jim's comments. That is why people have always built sacrifices to the gods, to keep them happy. He refers to this in lines 21-24. I don't remember Pan being destructive either-but we all have our bad days. That's an interesting comment about the destruction Pan causes.
EBB mentions the destruction and ruin in several stanzas.
Polyphemus was the cyclops dude and Circe did the oink magic. I think that Browning shows so much destruction, because we frequently become destructive in attempting to obtain what we want. Sometimes we are so bent on getting what we want and not being thwarted that we forget why we wanted it in the first place. But Pan destroys in his selfishness-thus the moral. I believe that EBB uses this descriptive techinque to show the reader that pan is more than a flute player and can be evil.