Excellent advice, Mike. I couldn't agree more. Riding when the trails are in bad condition is dangerous, harmful to the trails, and your bike gets coated in mud. It's lose, lose, lose. Please err on the side of caution, even if the trails are marked as open. Also, helping educate fellow riders (like you are doing with this post) should be a primary mission of club members. It doesn't make sense to promote mountain biking in our area if we don't also promote trail riding etiquette at the same time... in a way that makes sense and doesn't come across as overbearing or elitist. Even the most sustainably-minded trails will wear prematurely when ridden when conditions are unfavorable.
That said, I think the majority of people who ride are capable of making rational decisions, even if it means they don't get to ride that day. It's the few who don't know any better, or don't care. I think it's possible to reason with both types.
On a related note, I rode at Kettles this afternoon and evening, and found the opposite. Despite the recording saying the trails were open and in mostly good condition, the actual finding was somewhat different. In places I felt like it was borderline that the trails should have been open, or that I should be riding on them. If it was any worse, I would have sought out the quickest way back to the parking lot. It was a judgement call, which is really all you can ask of people.