"True Christianity"
That's too funny.
True Christianity. What is True Christianity?
Christians have been calling each other's beliefs heretical and schismatic for roughly 1,800 years.
Emperor Constantine convened the First Nicene Council in 325 CE to nail down "True Christianity", and immediately disputes broke out.
Eastern Orthodox and Roman Catholic Christians got into a dispute over whether the Holy Spirit proceeds from the Father and the Son, or just from the Father. That caused the two main divisions of the Christian Church of the time to split, each proclaiming itself to be the One True Church.
Then came Martin Luther and John Calvin and a bunch of other people, each proclaiming their own version of Protestantism is the denomination closest to what Jesus wanted.
And for hundreds of years, Protestants fought Roman Catholics, and vice versa, and each other.
The beauty of the American government is that it treats all religions the same, and ideally keeps them at arm's length.