Why do Black guys act like i'm doing some sort of unspeakable act ....?

when they find out my man is white?? i'm mixed and none of my mixture is african american to begin with...so what if i date white guys...just happens like that...Do i really have to be lectured about it by someone who just wants my number? And why do they make it sound like dating a white guy is an avoidable medical condition "Awww now why you wanna go ans do taht to yourself" Am I dying of caucasian-itis? PLEASE ANSWER MY Q's it may be life or death