Like with any religion, there are those at all stages of development within them. Even though the religion may teach a pluralistic attitude, the tribal ethnocentric mentality is what comes first before that level of inclusiveness is actually embodied by the individual. Given the position of power, as you point out, whatever the dominant center of gravity is will prevail. Then a "universal religion", like Christianity was intended to be, becomes a force of domination of others.Generally we don't actually know until a group is in the majority. The Buddhist have a very peaceful philosophy, but look what happened in Sri Lanka, and in Myanmar. The Baha'is would be foolish to go to arms in Iran. If they were in a majority situation somewhere, (yes that's a big 'if') and there was an armed rebellion, how could they put it down in a peaceful way? So we may never know.
It's inevitable. It's the nature of any group dynamics, and the highest level teachings, become interpreted as "kill the infidels". It's not simply a matter of being taught higher truths. Education comes from growing into them, not having them poured into you or written in your scriptures. It is always understood by the level of the individual, or the group, that is reading them. You think Christians actually get what Jesus was saying? Very few do, I'm convinced. The same applies to the Baha'i'. It applies across the board.