Cocoa is pretty fat and (at least in Italy) there is a popular belief that it might cause acne.

I think it's also interesting to note that Nutella (also from Ferrero) has a history of being a post-WW2 pure chocolate substitute at a time when hazelnuts were much cheaper and easier to source. It seems to be in the company's DNA to produce chocolate-based confections while touting chocolate as the bad guy.

Cocoa powder is just fat and carbs with basically no other nutritional content but it's not really any worse for you than other sources of the same thing.

The milk is probably the most nutritionally rich thing in your average chocolate bar.