I'm assuming this is a dig at Apple. Care to show that any other laptop manufacturer's webcams are impervious to having their firmware overwritten?
First: peer review. If your design documents are readily available, researchers don't have to reverse engineer them. Also, by open sourcing hardware design you lower the bar for critique: you might get feedback from an experienced electrical engineer who might not know how to write and upload a custom firmware for a USB controller.
Second: you can easily change it because it's not a black box.