Christianity (at least protestant) is apolitical and personal faith, any cults that claims to be championing political movements or claim God's support behind genocidal regimes are just that, cults.
High tens of millions seem to be a reasonable estimate of how many Christians are in China, almost all of them being just normal people from different walks of life, including politicians. Politicians are not allowed to show favor in official settings to any 1 faith, it's something that has to stay in their personal life.
I don't think there's anything more problematic with Christianity as with Islam or Buddhism. In the past, "Christian" regimes created some of the most dystopian and oppressive conditions in the world, but same can be said for Buddhism under the Gelug sect. The lesson is that religion should always stay out of the government, and cults that try to control their members should be eradicated.
