Maybe the title should be "What can Facebook learn from WeChat?"

Wechat has no ads because the government uses it to spy on almost everything you are doing from paying a parking ticket to purchasing groceries. It has replaced cash in many areas of China.

It's also tightly controlled and censored.

I would much rather have advertisers trying to sell me something than a totalitarian government using it to control my life.

Your life will not be disturbed until you use it to commit a crime.

Or maybe attend a peaceful protest asking for political change.

Fair enough, but also keep in mind that what constitutes a crime changes over time and culture. The law is also vulnerable to interpretation, for better or for worse, by those who enforce it.