Based on context, I think it's clear that stinkytaco was talking about things like high-fructose corn syrup and corn chips and corn-based cereals, as "corn byproducts," opposed to unprocessed vegetables and fruits.
If we're being pedantic, though, corn is a grain, not a vegetable (probably).[1] But that's clearly not what you meant, so it's not really worth digging into.
> high-fructose corn syrup and corn chips and corn-based cereals
These are bad to the extent they're calorie-dense and nutrient-poor, which most First-Worlders don't need. They're like honey in that respect. Corn isn't the problem.
There's been speculation about whether fructose and glucose have differing effects on satiety and insulin resistance, but the studies I've seen were conflicting. I assume it's possible to make high-fructose syrup out of other starches, and corn is only associated because it's cheap and commonly used.
If we're being pedantic, though, corn is a grain, not a vegetable (probably).[1] But that's clearly not what you meant, so it's not really worth digging into.
[1]http://empirezone.blogs.nytimes.com/2007/06/11/corn-vegetabl...