Diversity has done a lot for people's self esteem, especially groups that have been stigmatized or made to feel insignificant because they lack a certain pedigree. But I often think that diversity in literature has benefited girls/women a lot more than boys/men.
One prime example I have is of women-both white and colored- having white male love interests and very rarely did I encounter books that have a non-white male as romantic interest. I imagine years down the road that my son might discover girls in his teens, and perhaps he might have a crush on a girl. He will try to approach the girl, only to get shot down, or else hear the dreaded words: "I don't date Asian or half-Asian men. I date only white guys." Following that, I imagine I will be in a quandary between trying to boost my son's self-esteem versus what society is telling him; that he is less than because his father happened to be of Chinese ancestry. And if he becomes interested in reading, I honestly will have a lot of difficulty in coming up with age appropriate books where the Asian/ half-Asian hero ultimately gets the girl of his dreams.
If I feel this way and my son is only a year old, I can only imagine how other parents with teen boys who aren't white feel; how can a mother help her son build his self esteem, tell him he is worth it and deserves the best when in books and movies and in majority of TV shows the son rarely sees himself as the hero but only as a sidekick?
In my experience, the emotion is not pleasant and it's very alienating; it becomes a box that keeps you from trying to relate to others and to be human; it also does not address any elephants in the room and doesn't help break down barriers between people.
I also believe that lack of PoC male heroes prevents many boys from reading fiction unless it becomes absolutely necessary. If a person doesn't see themselves represented on television or in reading literature, then that medium is most likely to be abandoned. (One main reason I don't care for American TV) and because people in America care more for TV than for reading, it's much easier to drop reading than TV.
Believe it or not, but lack of non-white men in books and literature also affects how women feel about men and of how women feel about themselves. What do I mean by that? Allow me to explain: when I was growing up, I was embarrassed about myself simply because my love interests were Asian men. Society tells women that non-white men are not and should not be desirable; that they are either over-sexed or sexless, and they are not full human beings. When society tells someone one thing, but the person feels differently, a war inside of them will begin and there will be one of the two outcomes: either woman will reject her own emotions and fall in line, or else the woman will accept herself but will alienate society's rules and will not feel connected to others.
Lack of non-white men as heroes or as romantic leads also leads to status quo of white men being seen as better than non-white men, and it closes a lot of fascinating stories that could result from pursuit of the heroine and of how the non-white hero managed to conquer various obstacles and be happy.
Ultimately, I would love to see more books where the male love interest is non-white so I can tell my son that yes, society does see him as an extraordinary human being instead of something less than, and that he can get the girl of his dreams.