We want your privacy to be respected and your presentations to only be available to you unless you decide to share them with the world. The default mode when you create a new deck is Private which means that only you can see the contents of the presentation.
Even though you already have a link to share with anyone from the moment you create a deck, they won't be able to view the presentation unless you've set it to public or share it with them privately. Instead, they will see the following error page:
Tip: You have to be logged in to view your own private presentations.