What are you defining as a supplement? Some foods, are labeled as supplements due to federal laws and such, when they are really a FOOD and not a supplement.
I agree that with an ideal diet, supplementation is unnecessary, BUT good nutrition is tough these days even for the strict organic consumer... unless of course you have full control over everything you put in your mouth (which we do not, because our soil and pollution content of the rain is not under our control), from seed or conception (if you are a meat eater) to stomach.
I do think that supplementation can be very acid forming and dangerous if we do not know what we are doing...