Despite the strong association of the term with collective Jewish guilt and concomitant slaughter, Sarah Palin has every right to use it. The expression may be used whenever an amorphous mass is collectively accused of being murderers or accessories to murder.
The abominable element of the blood libel is not that it was used to accuse Jews, but that it was used to accuse innocent Jews—their innocence, rather than their Jewishness, being the operative point. Had the Jews been guilty of any of these heinous acts, the charge would not have been a libel.