But beyond that the amount of such voices I wittnessed in my feeds also isn't too small and I neither followed Greta Thunberg nor do I have many environmentalists in my feeds.
Literally every news article daring to mentioning her had 40-50+ "critical" voices with a perceived majority of men that could have been her father.
So all of what I say here is obviously very subjective and I am convinced that you are right, when you speak of a loud minority. What fascinated me is how middle aged men go and under their real name rant about a 16 year old girl and still feel like they are doing the right thing. And I don't mean trolls, I mean guys that really do think this is what they need to do.
Myself I didn't really deal with Greta Thunberg. I think it is nice that she creates attention for this important topic, espcially among audiences who wouldn't be reached by pure scientific publications, but personally I am not that interested in what she says, because her points are mostly moral and ethical and I agree with the general idea that we need to drastically change things even if it hurts.
I haven't heard about that (and can't find it). How many people were burning posters? If it was just a few, that's another example of the amplification I mentioned. A few crazy people are elevated as representative of the opposition.
The Washington Post ran a story like that. "Swedish climate activist Greta Thunberg is sailing to America amid a storm of online attacks"[1]. Their evidence for that "storm"? Three tweets.
1: https://www.washingtonpost.com/world/2019/08/15/swedish-clim...