A few issues I’ve heard about included higher rates of mental disorders, depression, etc. If they’re lucky enough to avoid that, then there’s the issue of not being able to get life-saving surgical procedures due to how unique they are. A white mother and white father have a better chance of being able to donate an organ or bone marrow for their child, but parents of a mixed child are so far removed from their own child that there’s no compatibility to be had - the child would need a donation from another mixed person. Edit: disclaimer: I’m just some asshole on the internet. Please question me and do your own research.