Hoist by one's own petard of "logic"

This widely-retold story is so classic, it's probably spurious. Nonetheless, it’s a good example of quod erat demonstrandum (QED) logic:

 A Republican state convention delegate speaks with a Utah GOP elected officeholder about immigration. The delegate argues that a fence should be constructed to span the entire USA-Mexican border to keep out illegal immigrants.
 GOP OFFICIAL: What happens when they climb the fence?
 DELEGATE: You electrify it. Then they won't touch it.
 GOP OFFICIAL: But what if they touch it? You would let them die?
 DELEGATE: It would be their choice.
 GOP OFFICIAL: What about a mother with a baby strapped to her back? You would let the mother and the baby die?
 DELEGATE: It would be the mother's choice to kill that baby.
 GOP OFFICIAL: Then you're in favor of abortion?
 [Silence.]

Sophistry for the Unsophisticated

Over at NPR, there's a piece up about the impact new gun laws are having on some weapons manufacturers. It yields this priceless bit:

Lawrence Keane of the National Shooting Sports Foundation, an industry trade association based in Newtown, Conn. He says the state's new gun law is misguided because it will only affect law-abiding gun owners.

Now try using this justification for ANY other law and see how silly it sounds.
—"Our new stop signs are misguided because they only affect law-abiding drivers.”
—"When you outlaw embezzlement, only outlaws will embezzle.”
—"Spun honey is inhumane and must be banned. Do you have any idea of what a centrifuge does to a beehive?”