How are they going not to? Hand-verify each provider and each claim? Not scalable and volatile, reliable site today can become trashy in two years. It's either completely uncurated list (welcome, 4chan trolls, food bonanza for you!) or list curated according to biases of a small overworked team isolated somewhere deep in the guts of Google corporate behemoth. What other options are there for selection?
> They are providing markup so they can associate claims of fact with identities
URLs already provide that markup. Google's markup assigns specific elevated role to "fact-checkers", implying they are somehow more authoritative than the original article, otherwise there won't be any need for special designated status for them.
> They can then choose how to weight those claims using other evidence.
That's what I am afraid of - that they (Google) would choose to weight the claims according to how they see fit, thus blocking from me information they consider not necessary for me and skewing my informational stream.
This does not look like a good setup to structure the discussion. Why somebody would get so much authority just for using some API? It's like giving people password-less sudo access and then wondering will it work well.