Final answer:
The idea in the 6th stanza is that beauty is subjective and the ability to see beauty in something harmful is universal.
Step-by-step explanation:
The idea in the 6th stanza is that beauty is subjective and the ability to see beauty in something harmful is universal. This is suggested by the connection between the ribbons in the first stanza and the flames in the second stanza, both of which appear beautiful to the speaker and the believers even though they are pollution and destructive.