It's a culture VS religion thing. While religion is a big part of a culture and it influences it a lot, many of its ideals also contradict the secular ideals. And the people who say Christianity is the most tolerant religion they do so because in their minds christianity is part of the western culture (which is supposed to be progressive, liberal, tolerant and all that). But did the actual people who helped and still help bring change and progress and open mindedness do so because they were christians? Because their religion told them so? Maybe in some cases yes, but definitely not in most of them.
People will be open minded only when it's about something that affects them, but not their neighbour. Christians think they are because they accept people in church in just jeans and because they don't stone people who have sex before marriage anymore. But that is because those changes are to their own advantage, not because they finally became tolerant.
