>But how do they justify this when their personal economic well-being requires trampling the freedom of other people?

There are 3 great evils in China: terrorism, separatism and extremism. HK/Tibet/XinJiang/Taiwan are not economic issues but security ones. People balance prosperity for security everywhere. The west sees HK as a large pro democracy movement, the Chinese see's this as fringe separatist violence by 0.001% of the population. They see HK as Chinese alt-right getting bold undermining domestic serenity: disenfranchised, social media savvy, economically anxious youth who see their culture being displaced and their privileged being eroded by mainland immigrants. They're acting accordingly.