I understand what you are saying but I'm not completely sure I agree, at least in principal. Is a company really affected by it's staff expressing their views? Perhaps to some degree, but I would suggest that companies manage to survive quite well after serious screw ups (cadbury's and ecoli, tesco's fresh meat scandal not the horsemeat one, hsbc's dodgy dealings with tax evasion and helping launder money and many many more) so how much damage can a pleb do by expressing an opinion? Company execs cause huge amounts of damage to a companies reputation through piss poor management, collect a handsome salary, rebrand and it's all good the following day yet one poor sod can topple an empire with a rant on fb? I'm not convinced.
How different it is that I post a comment on my fb page with my employer listed vs unlisted but where everyone knows who I work for anyway.
Not trying to be argumentative, I just think I can see both sides of this one and I think I would come down on the side that says the bigger harm is in restricting a persons ability to express their views. I just don't see that it is something a company \ employer can have a right to control outside of work. Unless they wish to pay me 24x7 perhaps.
As for anonomity and my employer, technically I am my own employer :-) but I do prefer a firewall lest my clients find out I am a closet nerd ;-)
In reality it's more to do with being a private person, but you are correct, it's a useful precaution and can serve many purposes.