Guess I forgot the category exemplified by the song chico posted about Harriet Beecher Stowe (on 13 Jul 06 - 08:43 PM and 08:51 PM ):

Songs critical of abolitionists -- in general or by name -- accusing them of hypocrisy, ridiculing them, etc.

(In the case of the songs chico posted about Stowe and John Brown, I suppose that they could also fall into the "warnings" category: warnings against becoming an abolitionist lest you be rebuffed by royalty, jailed, executed, sent to Hell, etc.)