You protect your data by not letting other people see it.
Someone will have to see your data sooner or later. An institution that you would normally trust not to steal from you would be under no obligation to do so. If you have a bank account, someone (or something), somewhere has to know your personal details, even if only fleetingly. What if they took that data, and told everyone? By your argument, that data isn't yours. If you wanted any guarantee that your money would stay yours, you would have to keep it in cash form all the time, in your house. Sure it could work for some people, but others prefer not to be so paralysed with justifiable fear for their savings. Essentially, we would be putting a reasonable doctrine (freedom of information) to its completely unreasonable extreme for no adequately explored reason, at the expense of our well being.