After careful consideration, this is my conclusion:
The reason I would leave a church that I've been with around for a while, is the same reason I have applied in the past: When the hindrance of proper evangelism becomes obvious, that the very church is the cause of it, it is time for me to leave that church.
With Chinese churches, the hindrance is usually in the context of 利害关系;
With American churches, the hindrance is usually in the context of Americanism.
Gospel-centeredness is the beating heart of a church, without it, the church heads towards senility, if not mutation or destruction.
When I posted this on Facebook, the likes and loves are mostly from people I least expected. So I am not sure if they get what I mean, if not, the word Gospel or Evangelism has really been diluted more than I thought.
However, on the other hand, it is a great starting point for evangelism. I have once used the problem of CCCNY as a curious talking topic with some non-believers and quite successfully at that.