But Greta Thunberg isn’t even rich or powerful - she doesn’t need ‘holding to account’.

Anyone who has political influence is fair game for criticism and opposition. You cannot have political entitles that are exempt from opposition. That's called totalitarianism. If we let you get away with that, you'll just use child human shields as your mouthpieces for every issue and then nobody will be allowed to dissent against you on any of those issues. That's absolutely depraved and the right must never reward such unscrupulous tactics by allowing them to work.