Because there was no way to tell that the reviewer wasn't being truthful.
@bonzo75 asked if he was successful; that depends IMO. He was successful in taking down someone that didn't bow to his will. But OTOH he's not been in the scene for many years. I've not mentioned a name simply because this was a long time ago and while I'm pretty sure I still remember his name, it would be nice to confirm it first.
Some of the other events I've mentioned I can name names pretty easily. And if someone wanted to sort out who I've been talking about it shouldn't be that hard to sort out, this being the Internet and all.
Human nature being what it is, if there are humans involved there's politics too no matter the field of endeavor.
For this reason and due to direct experience in the matter no-one is going to convince me that a negative review is ethical! About 30 years ago a speaker manufacturer drove out to our place from the east coast somewhere to show off his speaker to us. IMO it was terrible. I really didn't want to say anything to him as its not my way to offer insults if I can possibly avoid it. Later I saw the same speaker in a Listener magazine where it was taken to task over nearly everything wrong I had heard in it. Even though I was in agreement with what was written, I still felt the review should never have seen the light of day. If I had been in the reviewer's shoes I would have simply told the the designer that he has more work to do- that it 'seems promising but the promise is not yet fulfilled'. I know he spent a lot of money on that project and it was probably foolish for him to submit the product for review so early on it its design cycle. But the result of the review is the designer got wiped out.
He wasn't IMO a bad person. Did he deserve to get wiped out?
Being that I personally admired good designers it was imperative to me that when I finally submitted something for review that it would hold up under scrutiny. The one time it didn't was something I'll never forget- the reviewer liked the product so much he bought it. But we didn't advertise, so in a nutshell he was instructed to write something negative. After that he sold the unit (since he could no longer justify owning it after writing what he did). The new owner found it full of dead tubes; upon replacement with the originals we supplied (which were included in that sale) the unit worked perfectly. Now at this point I don't bear the reviewer any ill will; that was a long time ago and the simple matter is people make mistakes. But if not instructed by the editor of the magazine to write something negative he probably would not have, but as a junior member of the staff when the management tells you to do something you do it. Or maybe don't get to write for that magazine anymore. What I am saying here is that we're not just talking about reviewers, we are also talking about organizations and its a simple fact that to survive they all have to produce content. So they are often hungry for reviews and if the organization is dicey this could mean that the ethical issues get pushed aside.
Some more examples of why negative reviews are unethical:
* the product may have been malfunctioning possibly due to shipping damage
* the reviewer might not have it set up correctly
* the reviewer might have tampered with the product thinking he was helping out
* the reviewer might have a bias - such as 'doesn't like bass' (I experienced that one with a classical music reviewer) or doesn't like tubes or doesn't like solid state
* in the case of measurements the measurements may have been done incorrectly. I've experienced this on three occasions. In only one case was I able to get the review pulled prior to publication; that was in Glass Audio and I simply told Ed Dell that we would reveal that the measurement error was one speaker terminal being inadvertently grounded on the test bench, which causes our amps to have much higher distortion. But in the two other cases even when confronted with information like this the organizations proceeded anyway probably so they didn't have to redo their layouts.
A side comment: all things electrical obey Ohm's Law. It is therefore unusual that something like a power cord would not have some sort of effect. In fact they do and the results are easily measured; it should be no surprise that it can be audible too.