I'm not sure I agree that GI makes things complicated. I suspect it's sort of essential to proper hunger management. Blood sugar deltas seem to be a pretty major predictor for how strong the urge we have to snack is. That while we may feel yucky for having too high a blood sugar, when it starts to come down we still want to put fast carbs into our mouth (ironically perpetuating the yucky feeling from high blood sugar). By maintaining blood sugar through lower glycemic index foods, I suspect more people would find it easier to avoid snacking when they would prefer not to eat as many calories in a day. I know I personally liken eating fast carbs to "breaking the seal" when I haven't eaten for hours, particularly when last I had a good satiating meal with high nutritional content. I know that once I eat that first potato chip or cookie that I'll have a harder time not feeling the urge to continue snacking, so I like to put it off as long as my impulse control will allow it. Worse is when I'm not even hungry, but want the emotional rise of a fast carb. I can undo hours of good satiation from a meal with one slip...

But I suppose, your general assertion is fair. People who don't have a good sense of GI for food can't easily make some more complex decisions around food. For those people I tend to tell them to avoid processed ingredients. Anything that makes it easier for your body to digest, probably isn't helping with weight.