Are you sure about that? They would see it as medicine?
I have little doubt in my mind that opium in the time period being discussed would have been seen more in the light of medicine. Everything would have been based off first- and second-hand accounts; no scientific articles that dissected the properties of opium as we know them now, either as a medicine or a narcotic. I think a reasonable assumption for what a medical scholar during this time would think of opium is that it has very potent pain-relieving properties, but if the dosages are not controlled, it will lead to the patient becoming dependent on it, ill should it be taken away. What the average person would think of opium at this point would vary greatly, though I think it is reasonable to say that opium is used to dull pain would be the most common. It would likely be common knowledge opium could be abused, but I do believe the mindset prevalent here would be
too much opium can be too much of a good thing, instead of the opposite mindset today.
Given this, however, I think a valid point was made in how much this would actually historically impact a magical setting. If opium was used as a remedy for pain during recovery from an injury, and only the upper class could afford it, something that is present in this setting that would obviously impact opium's popularity as a pain medication would be the presence of healing magics. To which degree is very debatable, but personally, I don't have any problems with the setting's treatment of the legality of opium. Hitting on Barovia and Dementlieu... In the former, I find it very reasonable the Count would outlaw a substance that could draw Barovians away from their misery, and perhaps even becoming something that would hold more power over an addicted individual than fear of the Count. In Dementlieu, I find it less justifiable, but the reason Geiger gave pretty much covers how I would comfortably justify opium being outlawed there. However, common attitudes, I think, could stand to be much more flexible, especially in Dementlieu. In Barovia, if the premise is accepted that the Count would know about opium and its main effects (IMO, a logical premise granted Strahd is a highly intelligent ancient vampire), and it is outlawed based on this, then I think it would follow the majority of Barovians would simply comply out of fear of the Count, but not necessarily have a strong opinion of the matter. Common attitudes in Dementlieu would differ between the upper and lower class, I think. Some of the upper class might indulge from time to time simply because they can and it feels good, without really fearing retribution so long as they aren't blowing smoke in the face of a Gendarme, while others might look down on it as the peasants escape and have a low opinion of it. In the lower class, though, I have trouble thinking the opinion of opium would be anything other than largely favorable.
I'm grateful this has been brought up, because it does annoy me to see smoking opium equated to smoking marijuana, or seeing opium labeled simply as
bad, because in this time period, I don't think that would be the case unless a character had strong beliefs regarding opium, or negative experiences with it in the past. I can think of reasons why it may or may not be legal in specific places, so I'm actually quite indifferent on the legality of opium. Attitudes, like the topic title alludes to, are my main concern, and if they're to be played out, I'd like to see the same level of awareness and reason given to opinions on opium as any other matter.