On the topic of "people writing what they know", I have never found that to be a reasonable argument. Did Stephen Crane know the experience of a Civil War veteran when he wrote the Red Badge of Courage? Was Count Leo Tolstoy a Russian woman when he wrote Anna Karenina? What of Toni Morrison, did she have the firsthand experience of a black man in the mid 1900s when she wrote Song of Solomon? In each case, the answer is no, yet the reason they were able to succeed is that all three wrote their characters as part of the human experience. What I mean by this is, the characters were fleshed out, with their own motivations, ideals, worries, and joys, before ethnicity, nationality, and race come into play.
If one is worried that they will not "accurately" (Whatever this means) portray the minority group someone reccommends, research is always a valid option. The aforementioned Tolstoy spent years researching the battlefields and accounts of the Napoleon Wars so that he could write an accurate portrayal of it in War and Peace. Why not investigate, for example, how an average British minority (Of South Asian, West African, or Carribean descent) lived at the time period? Ask the descendants of those groups if they have personal accounts of their ancestors. Make it a learning experience.
However, even if one does not go to such lengths (Although it would be interesting) the most important aspect should be, again, to write a human, which any writer worth their salary should be able to do for any group of people.