That's called the 'contact hypothesis'. There's been a few studies that support it (including a famous one involving WWII soldiers' attitudes to mixed-race platoons) but most social science research has found the opposite.

Robert Putnam is the political scientist who's done the most work on this, and if you're curious, his most relevant paper is probably 'E Pluribus Unum: Diversity and Community in the Twenty-first Century'.

Putnam is an interesting academic - he was (and still is, I believe) utterly dismayed by the results of his research, but decided to publish it anyway.