That's quite interesting but shrewd leaders are often more keen on using piety as a tool when it aligns with their other goals. It's not clear if genuine moral panic caused them to send a "hard liner" to deal with the British of if was largely due to economic concerns in terms of paying for their armies and palaces.
The Daogong Emperor wasn't shrewd. He was weak and vacillating. He latched onto the explanation of Opium, that Opium was poisoning and ruining China, because China was in a terrible terrible situation and the Daogong Emperor felt helpless. A tremendous amount of civil unrest and civil wars was happening, the economy was in an incredibly precarious place due to China basically falling into a Malthusian trap that it couldnt get out of due to a stupidly high population and no industrialization. Hell, he even went to a shrine (of some sort, I forgot which), and asked his ancestors (or something else) what he did wrong, why was China like this? That was, If I remember correctly, the first time something like that has happened. Clearly, he was looking for answers.
Therefore, when the moralists argued forcefully that Opium was the cause of all of this because it was poisoning China, the Daogong Emperor latched onto it because it explained everything. It explained why there was so much civil unrest and revolts (poor morality caused by opium), it explained why there was so much corruption (greed caused by so much opium), a shit economy (opium), and just the general degeneration of the Chinese state (opium poisoning the people of China - morally, physically, and intellectually). Therefore, to stop that trend, the opium trade, which was already illegal, had to be crushed.
And it is quite clear from the sources and memorials that morality played a major factor in the decision, and was, in actuality, a greater factor in the minds of Chinese officials in the crackdown on opium. I mean, why the hell would these officials discuss at such great length amongst themselves and then with the emperor in private memorials about the evils of opium and the poisoning of China if they didnt believe it? It doesnt make much sense. A little posturing I can understand, but to go to that length, and considering the explanation in the previous paragraphs, the only logical conclusion, I think, is that morality played a major factor in the crack down.
I think your problem here is that you see society and history in economic terms and are projecting that view onto people who didnt. And when it is clear from the sources that they had other motivations, you think that that is simply posturing. I think that is a real problem because if you want to explain someone's motivations, then you have to understand the time, place, culture, society and individual viewpoints of individuals and realize that not everyone sees society only in terms of economic growth.
Hell, that is a constant criticism of Imperial China, that they didnt care about trade, put down merchants, etc etc, so I think it rather difficult to reconcile those two views. It seems pretty clear that you seem to hold a traditional view of Imperial China's view on trade and economy, and yet you try to explain their motivations for the opium crackdown as basically economic?