Why is it that a large segment of conservatives believe Obama is Kenyan based on a grandmother's claim?

My father claims that potatoes cause gout...well a decade ago, it was peaches....many family members are crazy, look at your own families and see if you disagree...claims are merely that, claims, those conservatives only agree with the crazy family member because it serves their twisted agenda. and yes, Obama has shown his Hawaiian birth certificate...so don't go there....