"Not liking an artist or performance and saying so is one thing (though I'd rather people said it in private or to the artist in a tactful, positive way). "

I agree with most of what you say especially with regard to the "suggestions" you mentioned.

However, surely the opinion of a listener, viewer, or audience member is just as valid as that of an official reviewer(journalist etc)whetehr favourable or not? Arguably, it ought to even more important what the actual public think?

As I've already said, I take the point about the one word comment but many paid reviewers can be extremely blunt and less than tactful too.