His resignation is being framed as a "freedom of speech" issue. It's not.
If he had been charged with a crime for what he said, that would have been a freedom of speech issue. If he had been sued for something he said, that would also be a freedom of speech issue. If he had been fired for something he said in his own time, that would arguably also be a freedom of speech issue.
This is about something he said at work, as part of his job, representing his employer. This is about how he does his job, and whether that is acceptable for his employer.
In the article above, Wallace Chapman explains that, while he hates what Paul Henry said, his job should have been protected from any consequences of what he says. I have the opposite opinion. I have no problem with anything Paul Henry has said (though I never watched his show), and while i agree that all speech should be protected from legal consequences, employers should be able to direct employees in the way they do their job - including the way they represent their employer while at work.
There was nothing wrong with firing Paul Henry.