Sorry, you're wrong. Private political opinions are protected from government retaliation, not from employer retaliation.
Pseudonyms are our friends. I hate to think how many jobs I won't be qualified for just because I've voiced controversial opinions under my real name.
Of course, if employers think defending marriage is controversial, perhaps they don't deserve my labor anyway.
That's a good point. I guess it depends on what the state laws are, and what the employer claims the cause of the dismissal is. If the laws say that the employer has to show just cause, and the cause is that the employer looked at the employee's private communications, the employee might have a lawsuit. If the employer claimed that he dismissed him for some other cause, that's different.