I’m not sure “rights” are the correct framing. The protesters surely expected to be fired. They traded their jobs for attention on an issue they cared about. The question of what is a legitimate protest, and when doing illegal things is tactically optimal, is quite a complex issue.
I think the only element of surprise/outrage was that seeming bystanders also got fired.
To understand this, consider Google’s position here; cynically it makes sense to use this as an opportunity for an “Object Lesson” (in Horowitz’s terminology). The decision to fire everyone here was obviously excessive, and that is the point. A proportionate response would not convey the message as clearly to staff. “Bring your whole self to work” is no longer the rule, this is clearly an attempt to signal that employees must yield to corporate values (or go elsewhere if they disagree). In other words the standard expectations from your employer, outside the SV bubble.