Agree, since crypto replaces the need for parties to trust each other with need to trust the system, actually banking on the 51% action would lead to the entire value of the system collapsing leading to loss of 'investment' for the one who managed to obtain 51%.

And this type of risk is nothing new and always have existed in any kind of social structures.

Also, while value should be based on gold and silver, it's not practical for precious metal to be used day to day by everyone so there needs to be an intermediary to serve as a mean of transaction.