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.

The free market works perfectly with perfect information.

I respectfully disagree. In a totally free market with perfectly free information, in certain markets, all it will guarantee is that people will know exactly how much they are being screwed by companies. Certain industries have high barriers of entry, or are highly susceptible to sabotage. Once companies occupy those markets, they can fix prices to their hearts' content.

What would actually work with perfect information would be a an over-regulated market. Companies wouldn't be able to put a toe over the line!

God helps those who help themselves.

(Apparently)

Ha! So true! A fine debut for your new account!