This isn't about free speech. Each one of the writers has the ability to write to their own blog, to tweet whatever they want. This is about some writers insisting that a company pays them money to write about whatever the writers want, instead of writing about what the people who are paying them want. That seems fine if the company agrees. I think some companies make that work, might even be a good idea. But if the company doesn't agree, well, I mean that's ok too, right? And the writers can quit if they don't like it (as they appear to have done), and good for them if they can achieve their vision elsewhere.
I think it would be wrong if the management was asking them to deceive people, or break laws. But presumably writing about sports is not abhorrent to any of the writers. Why all of a sudden did it become noble to tell your boss that they can't tell you what to do at work, for work related activities?
Am I a freedom fighter if I tell my boss that I'm not going to code that thing they want to get out the door next week, I have a pet project that I really like, and then me and all my other co-workers go on strike when I can't do that?