Can a diverse society not be a high trust one? It has been shown that more diversity is associated with less trust both among and within ethnic groups [1], but it still puzzles me why that is the case.
Diverse groups of people have different core values. What is treasured by some can be annoying or simply wrong for others. In such case, the best we can realistically hope for is "tolerance" - i.e. I don't agree with how you live and what you value, but I tolerate you in order to maintain peace. That's a suboptimal state when compared to true social cohesion.