If the things you say are true (which I'm unconvinced of), then it was dishonest/unethical of him to lie and withhold important and relevant information.
But there's no doubt that McDonald's is unhealthy and people shouldn't eat it. Which is why I thought he was doing a great thing by making the documentary even at risk to his own health and life, but if he was dishonest then I wouldn't say the ends justified the means of being dishonest.
The absolute truth is always of paramount importance for myriad subtle reasons that we're not necessarily consciously aware of (and of course also often for more overt reasons).