They're wrong to equate being remote with not producing value. If people are not producing value for the company, sure, fire them. If they are doing well, then why force them to relocate? What's the business sense in that?
They have $X in their budget. If the remote employees are producing $Y value, where $Y>$X, then they are earning their keep. But suppose Yahoo believes they can yield 1.5Y for the same $X budget by having on-site workers?
It's not like companies are (or should be) altruistic democracies. I can see why a person affected by this would be sore, but they don't really have a valid gripe IMO. I'm personally a fan of at-will employment.
So they were wrong to give them a warning that they are expected to relocate to an office? They should've just fired them? That's really how you feel?