Different threads were posted in order to clear up this question, but there are some points that I would need to confirm:
When you become a full-node (NOT miner, you just downloaded the full blockchain with a wallet or smilar), are you automatically a validator? Meaning that every new block will be validated by you (and the rest of full-nodes) in order to publish to everyone else whether is trusted or not. Or it does not exist someone that can be only a "validator", and only miners can be also validators?
Does block validation process spend too much energy? Or validate blocks is not a "big deal"?
In protocols that use PoW and PoS/DPoS (Bitcoin, Ethereum, Cardano, EOS...), once a block has been constructed using one of those consensus methods and included into the chain, will be always being involved this "second" validation for the rest of the full-nodes in that particular blockchain network? (I suspect that this second validation could be work slightly different in each of them, but always including this validation for the rest of the nodes)
And finally: what happen if one full-node start to rejects new blocks (he/she considers that are not valid), but the rest of the nodes says that is correct? Imagine a troll/hacker that starts to say that all the nodes are invalid, can that people be banned? Or will be that person just ignored?