Saying that eating large amounts of simple sugar is worse than small amounts of some of the banned drugs is one thing. But saying that sugar is poisonous, or simply worse than banned drugs, is a little too much.
I notice that you changed the text in the parents post from "some banned drugs" to "banned drugs", making the common mistake of grouping them all together and treating them as one category. (To me this indicates a fair amount of ignorance on the subject.)
Heart disease is the biggest killer in the UK, and I am assuming many other developed countries, so it could be could be easily argued that anything that causes obesity should be labeled more harmful than say psilocybin mushrooms, which I believe have very low toxicity. Just because they are banned, doesn't make psilocybin mushrooms harmful.
Though I might underestimate people's addiction, maybe there are IV glucose junkies out there now?
Then again, too much of nearly anything is bad. There are lots of known cases of people dying of drinking too much water, for example, but that doesn't make water a bad thing in itself.
Source: I gave a presentation once in middle school. ;)
Don't people remember the story of the woman who died drinking water to win a Nintendo? http://www.cbsnews.com/news/woman-dies-after-water-drinking-...