Theoretically, blockchains can be hacked but the effort required to do so is not worth the attempt at hacking the blockchains.
What needs to be found is a simple solution to create such significant frustration that it is not worth exploiting the system.
I understand I am suggesting a simple solution of a similar leap to that of the blockchain without giving any specifics. This is similar to suggesting there is a simple solution to mind control.
the solution hopefully may be simple... finding that solution I suspect will be very challenging. I am one of those that when I say challenging that doesn't mean I don't think it is worth the effort. I personally think challenging things are often the things that are most worth the effort.