The compelling argument is that it should be quite obvious that companies do not speak for all of their employees, cause most of them are - to what degree can be argued until the end of time - basically coerced to express the "opinion" of the company. At most it's the opinion of the owners, artificially amplified.

And to the question why the owners should not be able to express themselves: They can express themselves individually all they want, but if they want to use a company to do it they should also be personally responsible for everything the company does. And since one of the primary reasons to have a company is to isolate the owners from being sued personally ... there's a bit of a problem here.