You didn't just say to go on a whole foods diet, you suggested he become a vegan, which is a little bit more extreme.
My point, if you could get past the hyperbole, is that it is dangerous for someone to suggest that someone use some other alternative method of treatment in place of whatever the doctor is prescribing when they have little actual knowledge of treating illness, or the illness itself.
I'm not saying I completely disagree with your points, It's pretty obvious that the pharmaceutical industry is about making the big bucks. Why it is even legal for these prescription pills to advertise on television baffles the hell out of me... But, I wouldn't be giving medical advice.
People ask me all the time how I've lost weight, or blah blah blah. I tell them about my activity level and my diet, but I also tell them that there were a lot of other variables out of my own control that effected things.
Either way, I'm skeptical towards diet solutions, because it seems like every year some new fad diet(or old fad diet masquerading as something new) comes out, and people think it is bomb diggity. There is no doubt that what you eat effects the way your body works, but this is something for the individual to figure out for the most part. You have to shuffle through all the bullshit.
My diet of cheap liquor and cigarettes has done me fine, thank you very much.