You can't really call yourself a reliable friend of 'free speech' if your only concern is government censorship. Other forms of power and retaliation also suppress valuable speech.
Right, like covert, paid shilling, which is what is at issue here. If Coca-Cola got to write its own page, Wikipedia would be a lot less useful.
But is muzzling the entity and its spokespeople the truth-and-utility-maximizing response? It's suppressing information from the discussion, of which free speech advocates can be rightly suspicious.
Lots of paid work, even by people with an interest in the outcome, is useful. Until Wikipedia, all encyclopedias had mostly-paid authors. Almost all of the reliable sources Wikipedia uses have paid authors, often with a stronger-than-"NPOV" perspective.
If Coke wants to donate to Wikimedia foundation, or submit content to impartial editors, more power to them.