Why is there so much lashon hora on here about restaurants (and other things)

[biobook]

I disagree with your disagreement (opinion) and I'll explain why (evidence).

I definitely don’t think the burden should be on the reviewer to defend their review. Since it’s subjective anyone reading can draw whatever conclusions they want, as you did.

Contributing to a public site DOES impose a burden on the reviewer.  The expectation is that reviewers are altruistically providing opinions and facts that will help others make decisions about restaurants, and that requires the reviewer to think of OTHERS, not just themselves.  By posting on a site where people look for advice, one should provide advice that will be useful to others, and that may include having to explain WHY they were unhappy with a meal, so that others can understand whether or not it might apply to them. 

Maybe it was a discourteous waiter that triggered the reviewers discourteous reaction. After all, at a high end restaurant you might expect the waiter to remain professional even if the customer wasn’t.

Yes, I would have that expectation.

The reader of reviews needs to read them critically, considering to what extent any particular review might or might not apply to them.  Although I can't know whether the customer was at fault, the wording would lead me to rely less on this particular negative comment than I would on a more nuanced negative comment.

[madhocker]

Correct me if I'm wrong, but I was under the impression that whenever you express any negative info ltoeles, you are mechuyev to add any mitigating factors together with it.

You are correct. See CC 10 BMC 9.

[imayid2]

You are correct. See CC 10 BMC 9.

You are incorrect. That’s saying you can’t exaggerate the info. In our application the info isn’t more exaggerated by leaving out the “imo”

[madhocker]

You are incorrect. That’s saying you can’t exaggerate the info.

Read the BMC until the end.
ויודע שיש שום חלק זכות בענין המעשה הזה

[madhocker]

If it’s clear to all that it’s his opinion, as taste always is, I don’t particularly see the mitigation.
GS!!

This may be correct as well.

[imayid2]

Read the BMC until the end.
ויודע שיש שום חלק זכות בענין המעשה הזה

There is no need to be melamed zchus on pizza. If it didn’t taste good and you’re here to report that, that’s that.

[madhocker]

There is no need to be melamed zchus on pizza. If it didn’t taste good and you’re here to report that, that’s that.

He doesn't say melamed zchus. He says tzad zchus, which is another way of saying mitigating factor...

If you were to post an opinion but present it as fact (in a way that it is clear to the reader that it is a fact), that would be an equivalent to an exaggeration.
Again, if it is clear that it is only your opinion, I would be inclined to agree that it may not need to be disclosed בפירוש.

[mevinyavin]

I do not know specifically to which Halacha you are referring to. If it’s clear to all that it’s his opinion, as taste always is, I don’t particularly see the mitigation.

I am aware that taste is always an opinion, you are aware that taste is always an opinion, but IMHO you have to account for those who will read it uncritically. Talmidei Chachomim and those trained to read critically (lawyers?) will understand this, but we have a tendency to forget that most people don't read critically (as biobook pointed out above). Perhaps we will have to agree to disagree, but I stand by my opinion that one should point out it is only his/her take on the taste.
(For fun, I polled people over Shabbos asking if a statement regarding how good something tasted is viewed as a fact or an opinion, and everyone answered (x5), "I know that it is an opinion but no one else will read it that way, so you should emphasize it.")