Actually, I am trying to say quite the opposite. I am saying you should not be so dogmatic about the weight issue. People set goals for different reasons. It is your job to listen to the client and work with them to figure out what the reasons for losing weight are. Don't just tell them wanting to lose weight is the root of all social evil. You should educate them and direct them on the best strategy for achieving their goal. This may or may not involve weight loss.
The article is a meta analysis of all BMI to mortality studies performed around the world. So its pretty inclusive of what you are saying about obesity. Now, of course the evidence can be biased by the researchers, but I was simply referencing the article because you did. They said low level BMI obesity didn't lower or raise mortality but being OVERWEIGHT lowered mortality. Again these types of study basically summarize the results of every BMI-mortality study ever done. My point is not that we should encourage people to lose weight to live longer. I am saying we are arguing with the wrong tools. Our measure of obesity is not valid to determine mortality, but we shouldn't accept that as our final answer on the subject.