I agree with Guy on this one.
Any business should encourage sensible comment and even criticism – and be prepared to change where that shows concern in their customer base or to explain where they feel they are right.
My grandmother’s adage of ‘If you can’t say anything nice, don’t say anything’ is just useless over-politeness and inappropriate in these circumstances.
What IS needed is restraint by all members of a discussion group so that any contributor feels safe to criticise where they feel it is fair to do so and then take part in a civilised discussion if others disagree. Just like it is here !!!