It's actually not about legality. I didn't even suggest that.
>Just because a company has a right -- and an incentive -- to do something, doesn't mean that's a morally or ethically right thing to do.
As I said, it is expected to do it. Because companies have their own interests. The interests of the shareholders in Google's case. And Google is expected to act to protect them.
This includes getting rid of employees that act to sabotage the company, in this case by publicly badmouthing it.