why do we need diversity in society

(respectfully) I've never read someone who has speaks such sophistry with such conviction. Your reasoning for encouraging diversity can be summed up into "They bring fresh ideas and help us to understand our differences". Before I get into how ridiculously unfounded that reasoning is, let me first tell you that the rest of your article revolves around stating quotes from various leftist "researchers" and your own opinions, neither of which are reputable sources of evidence, nor are of any value to debate.

You, (understandably given the fact that your thoughts are young and malleable) are confusing diversity with multiculturalism. It is fair to say that to "have new experiences", you do not need a person from another country living in the house next to you. Cultural tourism is a very successful industry, but it's actually in decline. That's because we aren't achieving multiculturalism.

We're causing uniculturalism. As a British man, (straight and white; you must hate me. ), I can tell you in person that celebration of British culture is at an all time low. Traditions are side-lined to maintain "Social cohesion" with new arrivals, patriotism is "racist" and is bigotry. So when a white man stands up for western values, he gets shouted down by his countrymen for failing to acknowledge some "privilege" he has. The only "fresh" ideas migrants have provided are self-censorship, and self-loathing for the actions of our ancestors.

The rest of these migrants have surrendered their own cultures and assimilated a distorted version of our own, and we theirs, leaving a cultural wasteland, formally called uniculturalism. That's why tourism is on the decline. Foreign nations are becoming westernised, and are losing their charm. Western nations are becoming apologist regressives, and are losing our own identity.

With immigration, they either want to integrate, and lose their cultural charm, or they dont want to, and they become marginalised lunatics telling us how horrible we are.
Obviously, an open-ended question such as this has no single correct answer. I see the answer has many different ways of being answered. First, in society diversity can have t he evolutionary impact of genetically diverse people that would better allow successful copulation and passing on of beneficial genes.

Second, it has the social benefit of the spread of a variety of ideas or the enlightenment of others by conflicting beliefs. Third, diversity in society forces us to be more accepting of differences and to step outside one's own world to attempt to understand the unfamiliar. This exposes us to new ideas and ways of thinking which challenge and make us think about our beliefs.