said by sivran :

It's more like a prohibition-era speakeasy with a secret knock. Bang on the door like a policeman, and no one ever opens the little sliding window and asks for the password.

At the very worst, it's like having one extra password to enter. What could be so bad about that, aside from the annoyance factor?

Of course, physical analogies are somewhat flawed anyway. A door can be knocked down. A closed port (usually) can't be.