“Not only do modern methods of travel mean that the world's cultures are only a few hours away; but, thanks to radio, television and increased literacy, information about other cultures and religious communities is disseminated widely and rapidly. As a result, people in the modern world are increasingly aware of, influenced by and challenged by the existence of other religions and cultures.
Communities in which people shared the same religious beliefs and morality [...] are rapidly disappearing. [...] In modern societies there are few shared values to which one can appeal. Believers are constantly aware that their faith is chosen from a spectrum of beliefs on offer. Consequently, beliefs that were once taken for granted as exclusively and absolutely true seem increasingly implausible.”
It was easy, during the Crusades, to say that Muslims believed all kinds of evil, corrupt and immoral things. Because no-one actually knew any Muslims. With increased multi-culturalism comes increased compassion and humanitarian behavior towards those who are different. So it happens that when religious groups intermingle, illogical animosity decreases and it is no longer possible for one particular group to claim moral superiority when it becomes manifestly obvious that morals are cultural, and most religious believers are just as moral as anyone else, no matter if they're religious or not, or what denomination or religion they happen to have been born into. Believers will still believe that their religion is "correct", but moral assertions about different religious groups become impossible when such people are your next door neighbours and friends. The sociologist of religion, Steve Bruce, picks up on this theme:
“Every increase in competition makes that certainty, that dogmaticism, more and more difficult to maintain. If the competing faith belongs to some subordinate social minority, it can be dismissed as only fitting for that kind of people [... but when] you live and work with these people, it becomes more and more difficult to insist that your own link with God is unique and that the others are all wrong. Gradually, the way in which people hold their beliefs changes so that absolute certainty and intolerance diminish; the result is the denominational position of supposing that all these organizations in their different ways, are doing God's work.”
"Religion in the Modern World: From Cathedrals to Cults" by Steve Bruce (1996) [Book Review]3
Increased tolerance for different religions, ethnic groups and beliefs is incompatible with fundamentalist beliefs about your own religion, sect or cult being infallible or chosen to the extent that other people don't matter - only their beliefs. Isolated religious groups or areas where a particular religion is overly dominant can regress to this type of behavior though, but multiculturalism and modern freedom of movement and speech hopefully makes this less likely, especially in Europe and the advanced modern East. A surge in cultic isolationism, ghetto-formation and reactive rejection of the world, unfortunately, means that some people go the opposite way and in pluralistic societies, hardcore groups of extremists can emerge. See my page The Causes of Fundamentalism, Intolerance and Extremism in World Religions, and Some Solutions for more on this type of reaction.
Aside from the generation of small splinter groups of extremists, pluralism can otherwise cause entire religious denominations to rethink their relationship towards those who believe different things. A scholar of comparative religion, M. Momen, states:
“One way of dealing with the problem of modernity and religious pluralism is to withdraw from making any universal and social claims for religion, thus making it a purely personal affair. 'My religion satisfies my needs. It may not satisfy your needs or even anyone else's. All that matters to me is that it satisfies mine.' This then sets up a defensive wall against any possibility that one's religion can be shown to be intellectually faulty, illogical, or inferior to another's.”
Multiculturalism takes away from the powers of preachers to reassure the followers that they're inherently better than others, it defangs the aggressive notions that one religion is "better" than others in social terms. As a result of multiculturalism, people live in a world where they can change religion, change beliefs and they are not going against all of society. They know that they are not alone because of all the religions apparent in the nation around them; they know many people who are not the same religion. It makes freedom of choice easier, and finally, it makes it perfectly possible to denounce religion altogether and continue life as a normal person without it.
The effect of multiculturalism on religious claims is not new to the modern world. The historian John William Draper, writing on this subject already in 1881, reminds us of some very similar effects taking place in the Roman Empire over 2000 years ago. Many of the perpetual wars between tribes and nations had been massively reduced, and instead struggled centered on trade, governance and religious beliefs.
“At the epoch of the transition of Rome from the republican to the imperial form of government, all the independent nationalities around the Mediterranean Sea had been brought under the control of that central power. [...] The perpetual wars they had maintained with each other came to an end. [...T]he conquering republic brought the gods of the vanquished peoples to Rome. With disdainful toleration, she permitted the worship of them all. That paramount authority exercised by each divinity in his original seat disappeared at once in the crowd of gods and goddesses among whom he had been brought.
If the destruction of paganism was completed when all the gods were brought to Rome and confronted there, now, when by our wonderful facilities of locomotion strange nations and conflicting religions are brought into common presence - the Mohammedan, the Buddhist, the Brahman - modifications of them all must ensue. In that conflict science alone will stand secure.”
"History of the Conflict Between Religion and Science" by John William Draper (1881)5
(1996) Religion in the Modern World: From Cathedrals to Cults. Oxford University Press, Oxford, UK [Book Review]
Draper, John William. (1811-1882)
(1881) History of the Conflict Between Religion and Science. 8th edition published by D. Appleston and Co, New York. Digital version accessed via Amazon.co.uk.
(2004, Ed.) Encyclopedia of New Religions. Hardback. Published by Lion Publishing, Oxford, UK.