I think it stands to reason that the thousands of self-proclaimed "Christian" religions, all teaching different doctrines, cannot all be true followers of Christ. In fact, Jesus said he would reject "Many [who] say to me...: ‘Lord, Lord, did we not prophesy in your name, and expel demons in your name, and perform many powerful works in your name?’ ... I will declare to them: ‘I never knew you! Get away from me, you workers of lawlessness." (Matthew 7:21-23) God's word warns that "there will also be false teachers among you. These will quietly bring in destructive sects, and they will even disown the owner who bought them, bringing speedy destruction upon themselves. Furthermore, many will follow their brazen conduct, and because of them the way of the truth will be spoken of abusively. Also, they will greedily exploit you with counterfeit words. But their judgment, decided long ago, is not moving slowly, and their destruction is not sleeping. ( 2 Peter 2:1-3) These and other Scriptures convince me that trying to mix true Christianity with false would only do harm to true Christians.