不对! The idea that Lin Zexu was "part of an internal powerplay between the Han and the Manchu, using the barbarians as a pawn" is simply untrue. The ruling dynasty had been in power for two hundred years; Manchu-Han relations had long ceased to be a major issue.
So why a mere nine years after the first anglo-chinese war finishes does the Han population of Nanjiang rise up and massacre the Manchu banner population?
Imperial China was under military occupation, it just so happens that the occupiers had the same coloured skin as the occupied.
The first anglo-chinese war occurs between the White Lotus Rebellion (1796-1804) and the Tiaping Rebellion (1850-64). Both are bloody Han uprisings against the Manchus, the later killing 1/8th of the civilian population (making it an attrocity of a scale rarely witnessed in the west).
Any idea that Imperial China is a settled happy state is erroneous.
And no, Lin was not sent to shut down all foreign trade. He was specifically charged with stopping the importation of opium, and it was Lin who had been chosen due to his strong anti-opium stance. Had the Daoguang Emperor wished to stop all foreign trade through Guangzhou, Lin would not have been his choice for imperial commissioner; again, he had been picked based on his previous campaigns to eradicate opium in other provinces.
So, why does he also attempt to shut down the salt trade?
The Imperial court is concerned with China, and with the apparent outflow of silver (although the high price of silver was actually a result of the earlier White Lotus rebellion, and indeed by the 1830's silver is being released back into the market from the hoards and the price is dropping dramatically). Whilst perhaps some were legitimatly concerned over the use of opium (and Lin is certainly sincere)
And as for Palmerston's letter, the "indignities put upon Her Majesty's Superintendent, and by the outrageous proceedings adopted towards Her Majesty's other subjects in China" that you cite refer to the Chinese blocking the exit from Guangzhou until Charles Elliott (the Superintendent) persuaded traders to turn over their opium, which Lin promptly destroyed.
No, the Opium was all handed over in early June 1839.
In October 1839 (4 months after the Opium issue was resolved in Lin's favour) Lin then expelled the British from the port of Canton and threatened to execute the entire crew of any merchantman not signing a Chinese bond. He despatched a naval squadron under Admiral Kuan to blockade the British in Hong Kong. Elliot's response was to have HMS Volage and HMS Hyacinth move to blockade any British trader from entering Canton and potentially precipitating a war, as the British constitution required British subjects to have a fair trial (and did allow other states to judge it's citizens, but Chinese justice was exceptionally corrupt), and he would have to intervene.
When a British merchantman attempted to run the blockade, the RN attempted to intercept, but the Chinese fleet blockading Hong Kong under Kuan moved to position to attack the port of Hong Kong and deployed fire rafts, after several warnings Elliot ordered them driven off, and a brief one sided battle occurred, ending as soon as the Chinese fleet sailed off.
It was this blatent Chinese aggression in October-November that precipitated Anglo-Indian intervention, not the Opium issue which had already been settled.
I'm going to leave it to someone else to refute your argument that opium is not particularly addictive; I don't know much about pharmaceuticals. But I do know my Chinese history. Clearly, you do not.
Yes, it's best to stick with the party line, questioning "China as victim" is liable to get you fired and exiled. I think, to quote Prof. Yuan Weishi, you've been "drinking the wolf's milk".