Look how Silicon Valley folks treated Brandon Eich when he made a donation to the majority side in a California proposition. It's not just academia where you can't speak freely.
The fact that other people are free to speak against you does not mean that you can't speak freely. Free speech does not mean freedom from having your speech acts criticized (quite the opposite; it includes freedom of others to criticize your speech acts.) And, yes, it means that your speech acts may affect your ability to hold a job where you are one of the major public faces of an organization (such as its CEO) and…
But hell no you should not deserve to get fired for donating to the Republican Party. You have the right to donate to whichever LEGAL organization you want.