Ruling with an iron fist tends to create resistance and without mass surveillance technology an unpopular regime couldn’t keep everyone in line. But if instead most people are in agreement about something being bad (like they are with slavery or pedophilia) then there is much less resistance to enforcement against it (whether that’s centralized or decentralized enforcement) and therefore that thing is more effectively stopped.

While lone individuals or small secretive groups could continue doing the bad practice, in terms of technology I don’t think this will matter much because they won’t be able to develop a lot of technology with only a small group of people who aren’t building on other people’s work and their technology also wouldn’t be adopted by a society that is against it.

No. I’m not convinced China is worse than the US in terms of developing anti-human technologies and people living in China can’t boycott China. The point is to get the people in every significant country (including China) to oppose these technologies so strongly that they aren’t able to be developed anywhere. The Chinese military has to employ Chinese people to make its weapons, but if 80% of the population is opposed to these weapons existing and even the foundation of modern technology on which they are built then that is going to be difficult. Even if they were able to only employ those who are fine with WMDs the public’s opposition to modern technology would be a problem for the government maintaining control while developing those weapons and forcing modern technology on the people as a means of controlling them.