I think it's more that the person thinks they don't like a product which they have never actually used.

Please note that this feature does not exist in isolation. Apple has not invented face unlock - nor have they invented reliable face unlock. You can unlock your Lumia 950 and Galaxy Note 8 (or 7 if you still have one) reliably with your face and it's just not as convenient or quick as using your finger because face unlock fundamentally is not as convenient as the fingerprint in my opinion.

I'm fine with "X says this, and Y disagrees" much more than "you're wrong for having an opinion". Also, I don't know about you, but I have disliked several products which I didn't purchase, and did not even try out. We're not all robots here ! :)

My issue is not that someone has an opinion on something they don’t own, as you said that’s perfectly reasonable because no one buys everything.

My annoyance is that people have an opinion on something that no one has used.

It’s perfectly fine to have an opinion about the Galaxy S8 without owning one. There were reviews and now there are other owners who you can look to find out how well parts of it work.

With the iPhone X we don’t even have refused to tell us if the feature works or not so complaints about it are pure conjecture.

I think it's more like... gah, now I have to drop a G because this tech is incrementally better, lets find ways so I don't have to do that.

People are entitled to their opinions, my issue is that right now no ones opinions are based on anything other than marketing and preconceive notions. And that means that some of these deep discussion threads about whether a feature works correctly or not aren’t productive in any way. But that’s not stopping anyone from bashing things.