Religious intolerance is intolerance against another's religious beliefs or practices.
The mere statement on the part of a religion that its own beliefs and practices are correct and any contrary beliefs incorrect does not in itself constitute intolerance (i.e., ideological intolerance). There are many cases throughout history of established religions tolerating other practices. Religious intolerance, rather, is when a group (e.g., a society, religious group, non-religious group) specifically refuses to tolerate practices, persons or beliefs on religious grounds (i.e., intolerance in practice).
It looks like intolerance is the new trend and a more horrible trend for the world's future can hardly be imagined. How might this poisonous trend be stopped? Fear and suspicion are powerful forces, but we have resources to combat them: clear consistent thinking; specific principles based on equal respect for human dignity and understanding.
Because intolerance is caused by fear, we also need to confront it on the emotional level, using everything we know about the workings of emotions such as fear, sympathy, disgust, and respect. One thing we know is that demonization of "the other" is far easier if people know nothing much about this "other," and have never been encouraged to think what the world looks like from that different viewpoint. In order to move beyond a climate of fear, then, we need more than good principles: we need the cultivation of sympathy, and therefore we need approaches through education and understanding, not just through argument and hatred.