[exo762]

There is a confusion in language used. Bitcoin has two types of actors: block consumers and block producers. Ethereum has three types of actors: block consumers, validators and block producers. Thing often described as "full node" does just that - it consumes blocks, checking if blocks are valid. Ethereum validators are different, they not only consume blocks, they also attest their correctness for the rest of the network.

[Rebelgecko]

Who validates the validators? The other validators?

[exo762]

No. Their role is a bit different. They exist to prevent so called nothing-at-stake attack. If each block has to be signed by known parties (parties selected in a way attackers can't control), and those parties are bound by slashing rules (signing two different blocks for the same height is grounds for slashing), than it is very hard to pull off nothing-at-stake attack and create an alternative chain.