The Quiet Food Critic
In the restaurant business, they say that its the quiet ones you need to watch out for because they will dislike something about your food, say nothing, and never come back.
Given the choice between a quiete critic and a loud one, I would always prefer the latter (assuming they have valid concerns). I would go as far as saying that the latter is performing a public service - both to the restaurant and to future patrons.
For the restaurant because they are getting feedback about their food and have a chance to make things right, and for future patrons because they are now being warned if not.
Unless you are a troll, there is both social stigma and a cost associated to your person when you leave negative feedback, especially publically. But for the person that is leaving honest negative feedback, they are doing a great service, often with no benefit to themselves (asides fron ranting).