Activation Lock really ties your device to your iCloud account, in a way that will make it very hard for bad guys to prep it for resale. As Apple explains in a few explanatory bullet points, in the fact sheet that appears when you update your device:
"Turning off Find My iPhone, erasing your device, reactivation, and signing out of iCloud requires your Apple ID password"
"A custom message can be displayed on your device even after a remote erase"
So any meddling will require your password, and you can feel free to wipe your phone and still send angry messages. The top lawyers from New York and San Francisco have sounded off on this new feature, calling it "an important first step towards ending the global epidemic of smartphone theft."