The one single fatal flaw is the "exclusivity" of each religion. They all claim truth, but they all call each other "heretical", and for all intents and purposes have been waging war with each other for some 3000 years.
So what? All tribal identities are exclusive. All nationalisms are exclusive. All ideologies are exclusive.
The Judeo-Christian-Islamic tradition has a single root. The parent religion was eclipsed back in the Roman occupation - just as were all other tribal religions in the empire. The elder son of Judaism - Christianity - was estranged from the father even before it was exported to Rome - and later split into Eastern and Western factions of Catholicism. The younger son grew out of local resistance against European occupation. These are
political entities with a religious front. So, eventually, was the third offspring: Protestantism. C vs P was the standard of warfare for centuries, just as C vs I had been for a previous centuries; now I vs P is most prevalent. Their flags are raised over fights for political power.
This is why Jesus had to die.
Jesus, if he ever existed, died along with countless rabble-rousers, insurgents and criminals the Roman legions strung up along the highways and on the hills of its empire. That happened three hundred years
before Christianity was was designated Rome's official religion. His execution had nothing to do with the exclusivity of Judaism (which applied only to Israelites, anyway: it's not a proselytizing religion).
He claimed to be the son of a God which was not acceptable by the religions in power at that time.
Nobody in Rome cared about that. They had an emperor who claimed to
be a god. Their gods had a tradition of fathering mortals.
The Hebrew priests didn't like him much, but nobody cared about them, either. There were little prophets all over the place, claiming all kinds of silly things, and nobody cared.
But there were also uprisings, and when any one rabble-rouser became too popular, the puppet government started to worry. Not being overthrown by the mob; about being perceived as ineffectual by the Roman authorities and replaced - or worse, cracked-down-on. It was necessary to keep order; to this end, an example had to be made of the occasional upstart.
This has nothing to do with heresy: that notion came later, when the RCC was consolidating its religious stranglehold over the empire. It was
all about power.