As long as you don't put partially hydrogenated oils or lead or anything poisonous in it, I say go for it.
I think that there is a place in the world for foods that are not entirely optimal, but nonetheless fine in small quantities in the context of a healthy diet.
It is not your responsibility to produce or sell items that would be maximally healthy for everyone, even if such a thing existed. It's not your responsibility to make sure that they consume your preserves in small quantities, or that their diets aren't already heavily skewed toward carbohydrates.
I don't have a big libertarian bent like some people on here, who will tell you "let people make their own choices on everything." I'm not against the idea of a soda tax, for example. But in your case, I think you are providing a genuine food that people can reasonably enjoy, whether as part of a healthy diet or a standard crappy diet.
The slippery slope of arguing that this is unethical is pretty absurd... is it ok for you to screen your movie? They'll probably be sitting during that time, which will shorten their hip flexors and make them less mobile, depress their metabolisms, and the movie itself will depress their neurological activity, thus making them less healthy and possibly decreasing their quality of life in future years, and negatively affecting the epigenetic outcomes for their grandchildren. Shame on you for offering any activity that isn't maximally healthy! ;)
Unlike the libertarians, however, I would draw the line somewhere before "anything goes and let people do what they want with their lives." I think it's unconscionable to sell things with trans fats in them, for example.