You can hide them with CSS. But then that would require some funny business in cases where you do want a ToC. Why do you want to hide all ToCs? They are meant to be a navigational tool. If your pages are long enough to have a ToC, I would think users would appreciate the help.
Personally, if I wanted to do what you're looking to do, I'd use Preset pages so when starting a new page, I select one with the NOTOC coding already in place. Just like the preset page with Placeholders. Then IF I want to have a TOC on that page, at time of Create New Page, I'd just erase the coding.