> If the laws were the same in the US, and I called Donald Trump an idiot, would I have to furnish an IQ test? If I wrote that Ballmer/Nadella was incompetent and Microsoft products are crap?
You can say all of that in England.
Before someone can take a case of defamation through the courts they have to show there's actual or probable serious harm. (For for-profit companies that would be serious monetary loss).
The defences are that the comment is true; or that it's honest opinion, or that it's a matter of public interest, or that it's in a privileged publication (which includes peer reviewed journals).
When you say "Trump is an idiot" he can't show any harm at all, let alone serious harm; and it's an opinion that many people have.
When you say "Ballmer / Nadella are incompetent" either they personally have to show serious harm (and they can't) or Microsoft has to show serious financial harm (and it can't). And it's an opinion that while strongly held and expressed is expressed by many people.
> but that the chilling effects caused by restricting speech are almost always greater.
If I take a photograph of you and make a flyer saying "XAA RAPES CHILDREN" and spread that around your workplace and your local community you probably want a few methods to make that stop. One would be harassment law. Another would be defamation law. This is really the only kind of thing stopped by English law.
(Are you aware that the English law changed in 2013? Are you talking about the old law? I agree that was terrible.)