It's not about whether Damore was trying to protect the company, it's about whether Damore was communicating with his coworkers about ways to improve working conditions. It is illegal to fire someone for doing so. Damore presents several ideas about improving working conditions, claiming this would also increase diversity. If I was paranoid I'd say he wrote the memo with the possibility of being illegally fired in mind, because it appears to have been written carefully with that angle in mind.