I'd argue that it is a perfectly legitimate thing for a singer to sing such songs.

I agree, but a wily fellow who has an eye on the possible outcomes of his singing will choose the subtle, more artistic approach, not the bludgeoning approach. That's the better way to get more people to consider your viewpoint. Show them a novel angle they might not have thought of.

Directly arguing a point in a polemical way is of course only one way of doing it, and not one which is generally the best. Doing it through a story, as with Vin's Linda, is more likely to work better - though if anything that leaves a singer even more open to the accusation of tugging at heart strings and trying to manipulate the listeners' emotions.

I'm not arguing against tugging at heartstrings in songs. A good song will always do that. I'm suggesting that a song that rattles on about little innocents, etc., is using a well-worn and unsubtle ploy oft resorted to by the kinds of anti-abortionists who help to get rows flaring up on forums by ignoring facts and preachifying instead. It's hackneyed and tiresome and there are better ways.

(And I know that pro-choicers are not always tactically squeaky clean either... ;-) )