The criticism of Greta on this thread has been so far polite and measured. She has received all sorts of appalling abuse, death threats and the like on social media, whereas this thread is simply taking issue with a view she expressed to her five million Twitter followers.
Greta Thunberg has a huge public platform. She has addressed the UN. She expresses strongly-held views that reach millions of people. She can expect, therefore, that people will engage with them and criticise them. I'm sure she knows this, and I doubt very much that she has a problem with it.
It seems massively condescending to me to say that Greta Thunberg should be exempt from criticism just because she's young, when she is clearly mature enough to meet government leaders and address huge public rallies.