Robert Putnam wrote a book, "Bowling Alone", about his research into the effects of di-VER-sity via multiculturalism on society. (And then he held up publishing it because he didn't want to do so without finding a way to "ameliorate" the ill-effects, then denied he did so, then accused people of twisting his words.)
What he concluded was that di-VER-sity and multiculturalism causes a deterioration of societal trust, even among members of the same racial/ethnic groups. People's trust in everybody is reduced, resulting in less "community" participation and activity. I haven't read the book, but I suspect this is because, even among one's own "group", one cannot anticipate whom one can trust to speak to honestly without having the other turn around and deride one as racist/sexist/bigoted/homophobic/etc.
Many conservatives-at-large will absolutely not admit that di-VER-sity is NOT our strength, that Black racism is rampant and very dangerous, that illegal aliens have not added a damn thing that is good to our country, and that islam is not a "religion" of peace and is at war with everything not itself, always was. Individual 'slims may be good people but there's no way to know which are poisonous without lengthy and frequent exposure and to my way of thinking, it just isn't worth the risk.
Now, one cannot be assured that saying that out loud, even in our Christian churches, will not result in being pilloried (and you'd THINK the massacres of Christians all over the world by muslims would be a prominent subject; it's not).