I don't think GP is saying nothing matters, they are objecting to the idea that the way to make systemic change happen is to convince individuals to change pers

I don't think GP is saying nothing matters, they are objecting to the idea that the way to make systemic change happen is to convince individuals to change personal behaviors through moral persuasion. We have, however, had some success at taking collective action; compare trying to convince individuals to make a moral decision not to use disposable technologies with a regulation that requires manufacturers to make their products repairable/recyclable/etc.