I think it's an interesting position for a society to be in - I used to work in participation, actively encouraging children whose lives were unduly affected by social services to get involved and participate and make changes. Many of them were very angry and passionately angry about issues that affected them.
In order for participation to work effectively, there has to be some tangible output. I'm not sure what Greta wants. She's angry and she's vocalising that quite clearly; but anger alone doesn't solve something. Does she want a children's parliament who can oversee what the adults are doing? Does she want a commissioning process, what does she think accountability is - and how does she think it's going to happen.
I have no problem with her passion and her drive, or even her inexperience. Often, young people are able to look at things in ways that adults cannot - but your point about the complexity here is well made, and continued anger without a plan a) leads nowhere and b) turns people off. There will be a minority group she appeals to - and she can show up, vent her thought of the day and then leave - but that's meaningless opposition.
I think if she genuinely wants to create some sort of change she needs to find her way into the political sphere and be given some of the difficult choices facing other people. She can't do the same schtick she did at 15 when shes 35 and has made no tangible difference other than 'raising awareness' in a rapidly fatiguing and diminishing audience.