A completely anonymous stranger has no way to prove that they're human that can't be imitated by an AI. We've even seen that, in some cases, AIs can look more human to humans than real humans do.
The only solution I can think of to that problem is some sort of provenance system. Even before AI, if some random person told me a thing, I'd ignore them; If my most trusted friend told me something, I'd believe them.
We're going to need a digital equivalent. If I see a post/article/comment I need my tech to automatically check the author and rank it based on their position in my trust network. I don't necessarily need to know their identity, but I do need to know their identity relative to me.