Hal, the same logic applies to these particular pro-lifers themselves.
You see, people operate by associations in their minds. How long does it take to forget the name of the not so obscure organization that had this stupid advertisement idea? How long until the story is repeated as "There were a bunch of stupid doughnut people who were totally pro choice?"
In this case, it doesn't really work like that. Many people think pro-life people are stupid, or they look down on them as "unenlightened" or whatever. By perpetuating this story of a small subset of them that ARE acting stupid, you strengthen that association and belief.
Abortion and donuts aren't associated in almost anyone's mind, so saying a bunch os stupid donut people are pro-choice would not make sense out of context, and doesn't perpetuate the already intense negative feelings people have over the subject of Abortion.