I think the reason that, as a group, we claim total responsibility for our weight, is that it gives us a feeling of being in control. If we let ourselves dwell on the possibility that some outside factor is responsible for our weight, we feel powerless.
I think both a belief in genetic/biochemical causes for obesity and a sense of personal responsibility for weight management can co-exist in harmony.
I totally agree.
Also I agree that it is not a level playing field, but that is true of lots of life issues.