The purpose of this button is to disable displacement maps in scenes where you do not know where the original author used them (like an evermotion scene). In your case you can simply turn of displacement in the render settings temporarily.
If I wanted to add an "enable" button I'd have to track all the states of all displacement maps in the scene (and save it somewhere). In the meantime, the user might be changing some of them or new ones will be added etc, this gets messy pretty quickly.