You can argue that the google dns can sign the answer with a cert you trust, thus you know you got the right answer. And then, when you get the address of the service you want to talk to, you can check their cert and know for sure you are again talking to the thing you want to talk to.
And here lies the problem, how are you going to check those certs? Are you going to queue at a google office and obtain a cert on a usb stick, then import that in you environment, then do the same for all other services you want to talk to? Or are you going to trust a central authority? What if this central authority is messing with you? What if someone up the chain is messing with your central?
Let's not talk about how your router might send your dns request to some guy's home server that answers to 8.8.8.8, instead of google and you can't do shit about it...
Everything we know about internet works the way it works, because everybody involved agrees to do the right thing, from ip routing, to dns resolving, to certs verifying. All of this is based on a set of rules set by a central authority, that everybody choses to follow. You can't speak about web decentralization as long as proving who you are is a very centralized system.
