I think one of the arguments is that so few people lead the Christian ideal of a saintly life and far more instead use Christianity as an opportunity to obnoxiously foist beliefs they may not full understand themselves upon others.
You're a relativist, then? That is to say, if most of us believed A=-A (an inherently false logical statement, or we could use if A then -A, instead) it might as well be true?
Unfortunately, we're not all on the same page, though. If I say to you, "hey, let's get some food" and you respond, "food does not exist", it's possible that you're right, but you're pretty clearly wrong in a practical sense, and we'll just get hungry. What I'm trying to say is, humanity can't
go anywhere if we can't all agree on certain things. They don't have to be true, but it helps. If you don't think humanity 'should' be "going" anywhere cooperatively, then we have nothing further to discuss and you may return to your tribe.
Another example: Suppose I use the Imperial system of measurement and you use the metric system. I send you specifications for a ship I've contracted you to build, but all the measurements are in feet, yards, pounds, etc. Since we have different systems of measurement, you could make a lot of conversions to bring everything into meters, grams, etc. but that's an inconvenience. Or, you could simply refuse to do business with me.
If we were both on the Imperial system, we wouldn't have to spend time/energy on this question and we could move on to other, arguably more important things. Likewise, if we were both on the metric system, we could do the same. The vast corpus of data already using each system aside, although the metric system has its "makes sense" merits, either one is viable, as are any number of other systems you or I could imagine up.
Which system we use doesn't really "matter" in a practical sense; it just helps if we use the same one.
Now back to worldviews. Human thought has a great variety of diverse viewpoints, and many of us are taught axiomatically to respect diversity because the current, diverse state is a "fact of life." However, on some levels, a diversity of viewpoints seems to be an enemy of getting anything done. If we were all rational-thought atheists, we wouldn't have to waste too much of our time foisting our ideas on others, since we'd just be preaching to the choir. The same goes for if we were all Christians, or any other religion.
On the flipside, you may respond that uniformity could be the enemy of the creative impulse and that useful critiques on the current state of things could be lost. That is a valid case.
While I'm not necessarily advocating that all persons should share all views, I'm trying to say that if all persons equally respected every and any possible view (the seeming ideal of the anti-"normative influence" train of thought), no segment of humanity could no longer accomplish anything in a cohesive social unit.
Finally, I would like to direct your attention to the story of the Tower of Babel. Just when humankind worked together and combined all our powers to become like the gods, God scattered us, muddled our minds, and gave us different languages so we couldn't conspire again so easily...