They do not understand how this is the same as a Muslim terrorist capturing an area and forcing everyone to convert to their specific brand of religion. What gives them the right to think their god is superior to other gods? Jesus is only greater in the mind of a Christian. To a Muslim he is just a prophet. To a traditional worshipper he is just a man from a faraway land. To an atheist just a great fiction at best.
What if a person who believes differently went round destroying Catholic parishes because they don’t believe in their own fiction? Would you not call it persecution and terrorism?