Lots of things are legal but maybe not what we want. I'd say a working culture where having the wrong political opinion can get you fired is definitely one of them.
There is no shield in the first Amendment.
Just because it is legal to say does not mean it should be said.
The shield is not there because there needs to be checks and balances on speech. While we do see unfortunate outcomes, review them. All those people had options.
People often cite the Mozilla event. It is not so often mentioned how a lot of people were going to leave.
Being a leader, in that example, carries with it some implications. People do not blindly follow in enough numbers to be a concern.
These are human dynamics. Legislating them, and or expecting people to deal en mass with others to the degree needed here is impractical.
There are risks and rewards in all aspects of life, very few sure things. We are nowhere near a state of society where it is possible to consider otherwise.