Seth Godin features a post on how to loose an argument. Personal favorites:

1. Forget the pitfalls of Godwin’s law. Any time you mention Hitler or even Communist China or Bill O’Reilly, you’ve lost.
2. Bring up the slippery slope. Actually, the slope isn’t that slippery. People don’t end up marrying dogs, becoming cannibals or harvesting organs because of changes in organization, technology or law.

Anytime I read a comment in the newspaper or on someone’s blog that features those two point I immediately stop reading or giving any intellectual credit to the writer.