Greta is fine at preaching to the choir. I highly doubt that there were people who did not agree with her, but then after listening to her speech, agreed with her.
MLK was preaching to the choir, for that matter. Many of his white listeners had a general belief that segregation was bad, but didn’t think they could change anything by themselves. When you get enough such people together, they start to act. Climate may be the same story, 50 years later.
