>Who the hell works somewhere and even cares enough about the company to protect it with literal stalking and threats? I

Some people would gladly do that for fun. There are lots of sick people who are looking for any justification to bully people. "Protecting" your employer would be good enough for them, especially if it comes with a bit of a cash bonus. It also gives them a bit of job security because the company will keep them around to do dirty work whenever it's needed.