It is OK to disagree or partially disagree with her opinion, as long as one has a good reason for that. But many people just actively hate her. If you go on her Twitter you'll know what I am saying.
I don't understand this. Some claim that she is just a puppy used by people who want to push their own agenda. I don't want to argue with that, but there are children in China and North Korea singing cringy brain-washing propaganda songs. They are obviously used by their governments as puppies. Would you hate those children?
Some guy told me that he hates Greta because she always looks so angry and never smiles. This is the most ridiculous reason that I have ever heard. Why would anyone expect her to smile all the time? I wonder if he is mistaking her for a J-pop idol or something, although I do believe that she probably smiles when climate issues are temporarily off her mind.
8-year-old Greta smiling (from her own Twitter)
I think there may be two hidden reasons why people hate her, but I can't be sure. First, there are people who always want to assert their authority in front of a child, and they don't want to be told by a child what to do. Second, there are those who are simply jealous of her, because what Greta has achieved dwarfs what many people (including myself) will be able to achieve in a lifetime. If this is the case, then it is these people that should be hated.
What I can conclude is only this: when it comes to liking or hating people, it is very difficult to do it rationally.