What does infected be the air whereon they ride And damned all those that trust them mean?

The phrase "infected be the air whereon they ride / And damned all those that trust them" suggests a deep mistrust and condemnation of those in power or authority. It implies that their influence is toxic and harmful, corrupting the environment and leading to the downfall of those who place their faith in them. The speaker expresses a desire for the downfall of these untrustworthy figures and a warning to others about the dangers of trusting them.