My Dutch colleague explained to me that national flag for Dutch people is not as important as for Chinese people. For Chinese people, the flag represents our country (but not our government). In our schools in China, we have a flag-raising ceremony every week. During the flag-raising, everybody stands still, because we love our country. The flag represents our country, and we want to show respect to our country.
Maybe you can't understand why the national flag is so important for us. In the Netherlands, I saw Dutch flags everywhere on the ground after Queens day in Amsterdam. So that's the culture difference.
You're free to say anything about human rights in China, but next time, before using our national flag, please take the culture difference into consideration.