Louis Rossmann, the Apple third party repair guy on Youtube, talked about how easy it was to damage an Apple screen in one of his videos the other day. Even if you eat over your Macbook (or whatever they are called) and the crumbs get between the screen and keyboard, the tiny crumbs are enough to crack the screen because of how tight the fit is when you close the laptop. So it makes sense that covering the camera might damage the screen, though I'd think a thin piece of tape wouldn't be as damaging as a crumb because the surface area of tape is more spread out than the tiny point of a crumb.