You don't need a zillion of full nodes to beware of frauds, illegal inflation, ... one full node suffices: It could publish a proof for any malfunction in the press and everybody would be informed! It is game theory, its basic "rational behavior" assumption, that is saving bitcoin right now.
One full node may be sufficient for one person, but if each user wants certainty that all the information they have is valid, they will each require a full node. Anything short of that introduces a requirement to trust a third party.
Nope. We don't live in solidarity, once there is proof that some entity is playing dirty, it is doomed, forever. We have the press, social media, etc. we don't need to do the test on our behalf. It is how the real world works.
My point: A full node keeps its own user from being defrauded (and become the example of a victim for the press) not bitcoin as a whole. Pools are not afraid of full nodes, they are afraid of losing funds because of the obvious social penalties like price falling near zero as a consequence of any misdemeanor.