".... it would seem to me that the obvious solution to this problem would be to ensure that you are not identifiable to the company when you are (in) the process of slagging them off - simple!!"
Wrong. You post on the internet (or even visit many web sites) they record your IP address. An aggrieved or offended party (including your employer) applies to an appropriate Court for an Order requiring the site publisher to release the IP address and your ISP to release your name and address. It has happened a number of times over the years with PPRuNe.
You have no anonymity when the law gets involved. Buai Bob, Check your PMs!
Criticise or libel your employer, even anonymously on the internet, and you are probably inviting termination of employment.
Solution: Don't post anything on PPRuNe, Facebook etc that you would not say or publish publicly in person.