"The British forcefully drugged an entire country"
It may be comforting to think in such simplistic black and white terms, but they weren't giving it away for free! Chinese traders gladly swapped tea for opium since there was huge Chinese demand. In fact opium production in China during this time skyrocketed, becoming far larger than imports by the end of the century. You may argue that it was immoral for the British to sell opium into China and I won't disagree, but the real reason Chinese authorities wanted to stop opium imports was simply protectionism (even though it was technically illicit). They wanted to protect the prices of opium produced internally and they were very happy for their own people to be drugged on their own supply.