[TZubiri]

So according to you, a picket fence or a wire fence is just a useless thing that makes things less usable by users?

Security does not consist only of 100% or 99.99% effective mechanisms, there needs to be a flow of information and an inherent risk, if you are only designing absolute barriers, then you are rarely considering the actual surface of relevant user interactions. A life form consisting only of skin might be very secure, but it's practically useless.