Businesses are more than happy to have positive reviews published on sites such as Yelp.com..hey, you can't beat free advertising.  However, a negative review is damaging....can't have that.  

This intersection of business interest and freedom of speech is interesting.  How about "word of mouth"..certainly not as widely impacting as an internet site posting, but just as damaging..maybe more so if it's a small business in a small community.  How about parents commenting critically in public about a teacher's performance, or disgruntled fans calling for the firing of a football coach.  

Perhaps, we need to adhere to the Thumper Rule: "If you can't say something nice, don't say nothing at all"