Can someone help me to understand why Google employees think they have some sort of first amendment rights there? Is it the culture / history of “do no evil” or

Can someone help me to understand why Google employees think they have some sort of first amendment rights there? Is it the culture / history of “do no evil” or the employees there feel especially privileged? Just seems like such a basic misunderstanding that you can say what you want without repercussions, being vocal isn’t a protected class.