I don't think that carbs or any conspiracy about carbs is to blame for obesity. People have been making bread for tens of thousands of years and obesity in the first world is a recent problem.
I think the fetish with eating 'low fat' as a way of not putting on fat is closer to the root of the problem. Basically Goverments and people themselves have confused low fat with 'low calorie.' So people think something isn't fattening just because it's got some fat taken out -despite it being full of sugar and whatever to stop it tasting like shit. Plus sugar is cheap bulk so it boosts profits.
If McDonald's etc pay to teach folks about good diet Tha doesn't make the information wrong. I think it's better than leaving people ignorant. Also I don't think it's as easy for big food to use junk science to pull the wool over your eyes now. The Internet has taken care of that.