I think it's sad, pointless and horrible, but not surprising, given that the US has a terrible record on racism, and in the 30s had a colour bar, Jim Crow laws and regular lynchings in some states. That was hardly going to evaporate when the army was based overseas, as it was woven into the fabric of society.
Also, the role of women in the UK was based on their relationships with men. They were (to generalise) seen in terms of the men in their lives, so someone's daughter, wife, mother, rather than as someone in their own right. Many married young, rape in marriage was legal, and the police rarely got involved in domestic violence. There would be lots of women who were unhappy, as well as those who did love their husbands/boyfriends but missed them - many had been away for years. Add in an influx of 'oversexed, overpaid and over here' GIs, and it's not hard to imagine that it would be a heady mix, particularly as the fact that life is short was so obvious, and people would be tempted to live for the day.
As contraception was unreliable there was always a chance of pregnancy, and a black baby would be incontrovertible evidence of an affair - a white one could be passed off as the husband's or boyfriend's. When women were judged by their sexual behaviour the risks would be huge.
The role of the government would be to keep the troops happy, which wouldn't happen if they were worrying about 'their women' going off with other men. Obviously that would apply regardless of colour, but inherent UK racism and the visibility of black babies would add to their fears.
None of that is to excuse racism, of course, but as ever, the context is important.