There is really no any religion is more insane than the other. Any ideology that claims itself as the absolute truth without any proper materialistic evidence or rational claim is completely insane. So it doesn't matter what theistic ideology one follows, they are all equally as absurd as the next one.
The problem lies on the believer itself. If one believes their doctrine is correct, then they will compare it another and ridicule the other as false and incorrect with the same fallacies and irrationality that can be said for the very same person's doctrine. But usually they are too ignorant to accept it. The insanity really comes from not only the belief system but also the followers acting upon it. Such as donating money to "reactivate" your mind in Scientology or teaching creationism or participating in violent martyrdom.
I guess you can say there are degrees of insanity but not really in theological cases. The reason someone might think Scientology is "more" insane than Christianity is because of societal and cultural brainwashing. In USA we are brought up in a culture where Christianity is the largest group, so automatically there is a phenomena that teachings of Christianity is the "truth". Anything else of that is considered wrong/insane. Now if we lived in a nation where Scientology was the majority, then we would think Christianity is wrong. This also ties into with propaganda. Scientology because of certain celebrities and what not, have a bad reputation. We see it in our media, always portraying Scientologists as weird and odd people. Kinda like with Muslims, its always violence, terrorism and oppression. Lot of Christians like to point out how insane Islam is and all, but they ignore the history of their own religion, which is filled with the same, if not, more violence.
That is definitely an interesting theory. However from what I learned in anthropology class, many of the early religions, specifically the ancient greek civilization during the paleolithic era, many of the religions beliefs had a purpose of identity rather than believing in a being for moral guidance. For example terracota figurines in ancient Greece represented mostly females and represented an offering to gods for good luck such as fertility to women.
One thing I would like to ask is, we Humans didn't really have oral language during the early Paleolithic era, about the time time when Homo Sapiens started to first appear. How would early mankind engage in any gossiping if oral or written language was not really established at the time.
I found this extremely interesting, and you might be able to glean from it something that may lend insight to your hypothesis: 5 things you probably didn't know about Neanderthals
Diminished social skills may have led to their extinction.
All religions are equally untrue and equally batshit.
Well, I don't know. Buddhist theory has some surprising (and perhaps coincidental) correlations with modern physics. For example that the everyday world of the senses is an illusion (reality is mostly empty space), that fundamentally the world consists of vibration (string theory), and so on. Certainly that is considerably less crazy than Scientology and the three Middle Eastern religions.
One man's religion is another man's (a theologian's) philosophy.
Sounds like you're interpreting Buddhist theory, to conform with modern scientific thinking, much as theists do with the Bible - "The Bible says god said, 'Let there be light,' then the Big Bang happened, and by god, there was light!"
For tens of thousands of years, delusional, insane people have been killing and eliminating from the gene pool, those people who do not share their delusions and insanity (ie. sane, rational, people). Thereby selecting for craziness. So, now we have a population with a propensity to be completely credulous.