I can't speak as to why other white boys like interracial, but I personally like it for two reasons: comperision and masochism.
From a comperision point of view, I believe/suspect that most white girls have a strong attraction for black men since black men are the ultimate "dark and handsome outsiders" that psychologically so many women find attractive. And I also believe that on average black men probably have larger cocks than white men and are probably better lovers.
With those assumptions in mind, I really get off on seeing white ladies enjoying a kind of sexual pleasure I can't give them (e.g., I experience compersion). I watch interracial porn and I think about my small penis and I wish I could watch a nice black man tenderly fuck my girlfriend. I feel strongly that she deserves the best sex possible and I want her to have a solid black bull who can fuck her brains out.
And then from a masochism point of view, I think there is a powerful sense of humiliation in seeing "your" women turned into whores for men of another race. For whatever reason, I find it intensely erotic to think about black men conquering and sexually dominating white women and fucking and owning my girlfriend, because I'm not man enough to compete.
