Quality chocolate is good for you, it's just that if you eat too much of it the calories get out of hand. Much like with nuts, they're a good source of all sorts of minerals but at something like 5-600 calories per 100g they're also a very good way to get fat.
Chocolate also contains phenylethylamines, which are chemically similar to substances the body produces when the person is in love. So when the Beatles sang their song they could have said "All you need is a good bar of quality dark chocolate, na na na na na"
When determining if a manufactured food is healthy or not, or in degrees of health, I find it best to ask a few simple questions:
Does it contain natural unrefined sweeteners - or extracted sweeteners or sweeteners made in a laboratory?
Is it fried or baked/boiled?
Does it contain hydrogenated or partially hydrogenated oils?
Does it contain "flavor enhancers"?
Does it contain artificial colors?
Are any of the products used GMO?
The questions beg binary answers, of course. And that's where knowledge and choice come in. Given the choice, I'd rather eat something that contains a flavor enhancer or is somewhat refined from a natural product (sugar cane, for example), than something that is deep fried or contains hydrogentated or partially hydrogenated oils or something that is completely lab-made for a sweetener or color.
But if those are my only 2 choices, best to eat something else entirely. Cocoa has properties that are healthy, that is true - but just because it is so does not make the overall food it is contained in healthy. Refined sugar is not a health food. It robs the body of minerals and vitamins that are taken out of the sugar cane when it is processed.
