It's a song that I have never felt able to sing, though at least one of the tunes associated with it (a Northern Irish one as it happens) was just too good to miss, so I use it instead for Lizzie Higgins' set of Willie's Fate, though obviously I always explain where it came from.

It's worth mentioning that accusations of the ritual sacrifice of children have always been a common propaganda ploy; as McGrath mentions, that accusation was levelled by Rome against Christians, and later, by the Christian church, against not only the Jews but also the Albigensians, the Cathars and the Knights Templar (amongst others), and helped to provide the excuse for at least one exercise in genocide directed against "heretic" christians.  More recently, exactly the same moral panic has been promulgated by mendacious propagandists of all kinds; both sides in the last two World Wars accused their opponents of eating babies, and the "Satanic Child Abuse" myth of recent years is an example of exactly the same thing.

Having said all that, I have always understood the "blood libel" to be the (undeserved) accusation against the Jewish nation of deicide; although clearly the song in question here is related to that, it is worth noting that it is by no means an unusual phenomenon in folklore.  To recognise all this ought to be to move toward a greater understanding of the prejudices which we all have some share in, and beyond which we need to grow.  We may perhaps best achieve this not by denying the past, but by trying to learn from it.  My main worry at the moment is that few nations (including Israel) appear to be in the slightest bit interested in doing that.