Yes, cocoa is a drug, but there's hardly any of the psychoactive substances in most chocolate confectionery items. To get serious amounts of it, you need really dark, bitter chocolate with >75% cocoa content. And anyone comparing it to heroin must be taking something much stronger.
Oh and cigarettes are only harmful because of all of the tar and nasty chemicals present in the smoke. Pure nicotine cause a similar level of harm as caffeine, so not good, but it doesn't cause cancer. Don't listen to all the BS propaganda about ecigs pushed by the tobacco companies.