They don't all subscribe to that way of thinking.
I see a lot more latina-black couples around here (austin and burbs) than white-black couples.
This is true, it is not an absolute distinction. However, what matters is when the Mexican Mafia or a cartel, for example, decides to cleanse an area, it is likely that a mixed race couple could get caught up in that.
This has happened a lot in Los Angeles. Often a black person is just walking down the street when there is a “warning drive-by”, not shooting at them, but near them, to send the message. So if they see the black partner, they will shoot near or at him.