Subjective opinions have different meaning to different individuals. For many people, they consider gathering subjective opinions, whether in a forum or from a review magazine, as a legitimate step in evaluating equipment. To those people, a subjective opinion by a "reputable" person can mean the difference between a sale, and not a sale for a given product.
When you give an opinion, like it or not, you are influencing the pocketbook of the vendor.
I'd suggest the following rule: If you would say it to their face, in a room at a show or at a place of business, then it is 'ok' to say it in their circle. It is wise to use tact, and to use the standard disclaimers that it is based upon your OPINION and give the context of your experience. A guy who owns the product should be given more weight than one who doesn't.
Of course I had some guy come up to me at VSAC and ask me why I lied on my web site and another tell me I'm not ready for "Prime Time".

I guess audiophiles are social misfits in general and don't know how to interact appropriately no matter the setting.