@resolute
Islam... but, for example, the Malleus Maleficarum (first edition of 1486) or the Code Noir (decree of French King Louis XIV of 1685) is also a "quality" perversion of Christianity.
Because Christianity also - more than once - failed totally, it was sometimes better for e.g. Protestants (in the aftermath of the Thirty Years' War) to flee to areas of the Ottoman Empire to avoid persecution from Roman Catholics. Islam, in my opinion, is neither better nor worse than Christianity, according to this assessment. One might even say that Islam does not even hide its dislike of "dissenters". The same actions by Christians are then accompanied, in my opinion, by greater hypocrisy and a more pronounced disconnect between the code of ethics and reality.
The question would be rather: why - despite good intentions - does it always fail like this?
Leaving aside the theological answer, I think the example of C.T. Russell is one answer. Notwithstanding his - not defective Christian ideas - he was guilty of taking his ideas as the "measure of all things". His individual beliefs, became a religion for others and a "measure" of right/wrong for others. Clearly others had a part in this as well, but the defining moment was sometime when he began to think he was an instrument of God. That he was - with all humility, which I do not deny - the chosen one, to proclaim his "truths" and pass them off as God's. This process was not an overnight thing, and if it occurred, then I think he also had plenty of time to "come back". At some point when his views began to be criticized (false prophecy, absurd exegesis of biblical texts, etc.). he should have "stepped on the brake" and tried to change/correct. But, I guess that couldn't be done. He had too much social "capital" invested in it and would have had to deny himself. But this completed his "turn" away from Christianity; in doing so, he laid the foundation for another religion that enslaved millions more (but it must be said here that despite the corruption of the gospel, the gospel still reached others; all is not lost! ).