I'm not sure Brecht would approve of the Bobby Darinized version at all. Here's Brecht himself singing:
http://www.youtube.com/watch?v=_QXJ3OXWaOY
Darin's version completely omits the parts about burning down orphanages and raping young widows. Then again, Darin's version also doesn't mention rich creamy shakes.
The basic purpose behind the ads: McD's isn't just for the little rugrats, it's a place where reasonably sophisticated adults can sit down for an evening meal.
How to convince them: A nightmarish lounge singing moonhead.