Modern people have a shallow and naïve view of culture. They assume that diversity of culture is always a good thing. After all, a variety of cuisines at a food fair cannot be a bad thing.
Cultural diversity can enrich a society, especially if culture is confined to different foods, clothing, music, art, dance, worship and religious festivals. Unfortunately, culture often goes much deeper and produces different attitudes to political authority, military force, violence, which make diversity a problem.
If religion is limited to cultural activities, then diversity of religion can enrich society. The problem is that religion at its best should go deeper. If religion produces different attitudes to family relationships, government authority, violence, war and property, religious diversity creates problems for a society.