I am married to a Jehovah's Witness and I attend an evangelical church. My beloved neighbour is Wicca. I've attended services of all three. You can imagine, with that proximity, that I've done some deep thinking on my own identity, what it means to be a Christian, and the dynamics of the taboos, prejudices, and prohibitions between these groups.
The demographic trend watchers lump us all together, you know.
We are all "spiritually minded", deeply religious, and typically entrenched in our views. So why is each group deeply opposed to the other? I know from visiting with my husband's religious friends, that they have a deep aversion to "Christendom". They consider us to be under Satan's influence and dangerously deluded. I must say my Christian peers feel the same about Jehovah's Witnesses. Few have darkened the door of the other because of that very fear. I've listened to urban legends from both sides of divine or demonic influence whenever a person has attempted to breach this terrifying barrier.
Take away the barrier, and what do you find? I've found the typical Jehovah's Witness meeting to be punctual, predictable, and dull. It "feels" more like a sales meeting than a religious service. "Worship" is relegated to scheduled, numbered songs. Supporting music comes from a CD. I've described the generic format of a Circuit Assembly, similarly dull, but eagerly anticipated by the average Witness. After all, it is one of the few annual events they may look forward to since they have been deprived of Christmas, Easter, Thanksgiving, etc., etc., etc.
So why the aversion, the terror? I talked about the power of groups to self-identify, even to the exclusion of others. There's the power of granfalloon. There's the risk that a religiously minded person, who has committed at great cost, to face the folly of their own choice. A "soft boundary" between the distinctions of religion would force us to give up distinctions that may not be there. Perhaps some of the traditions and forms are not so exclusive as we think. Strip all those forms away and what do we have? Self-delusion?
For most committed people, such a prospect is unacceptable. Better to exclude and avoid.
Or, perhaps, if we strip away the forms the substance will be laid bare. Maybe it is as simple as loving your neighbour, truly. Perhaps when all else is stripped away we are left with goodness.
Or, maybe, the easier choice is to blame it all on "Satan".