That does not logically follow from any point you've made. Preservation of something does not legitimize its theft.
If there were no Opium Wars, there would have been no Nine-Power Treaties, and thus the Qing would not have fallen, and thus Mao and the CPC would not have eventually gained control over China, and thus the Cultural Revolution and the Four-Olds Campaign would not have happened?
I am saying it's not legalized.
https://en.wikipedia.org/wiki/Tone_policing
The commenter was angry, but I understand his anger. I can see how even the slightest hint of it in sharing my personal experiences can trigger negative responses from other people, but it also helps for you and others to be sensitive to the trauma that many others (and our families) have lived through.
If I go to your house and beat you up, you have every right to call the police on me and they should be able to throw me in jail, and keep an eye on me until I've reformed my ways. However, this doesn't mean you can go to my house and start stealing all my things: just like any other immoral act, as you point out, one crime doesn't absolve another. This should apply even if you're a policeman.
Accordingly, the USSR should not have seized Kaliningrad, Stettin, and Silesia. Don't you think those territories should be returned to Germany?
If you come to my house and beat me up and loot my stuff, and then burn most of my house down, but I survive, and then a mob of poor people came by and then destroyed other artifacts in my house, do the actions of the mob of poor people absolve you, the original looter?
Does it complicate or simplify things if you, the original looter, also sold opium to the mob of poor people?