Trust isn't a binary relationship. Computer security is hard. I trust people to try their best to not get hacked or not to get kidnapped and tortured, but alas it sometimes happens. I'm surprised no-one has mentioned that the only reason to use a block chain is to achieve byzantine fault tolerance. Casper is trying to solve much the same thing that has already been solved by Tendermint but with different trade-offs (CAP theorem trade-offs).