The definition, according to UrbanDictionary.com -
A term that originated on Usenet, Godwin's Law states that as an online argument grows longer and more heated, it becomes increasingly likely that somebody will bring up Adolf Hitler or the Nazis. When such an event occurs, the person guilty of invoking Godwin's Law has effectively forfieted [sic] the argument.
Basically, a "Nazi" or "Hitler" analogy is used when a person involved in an argument wants to associate something they disagree with to what was recognized as perhaps the greatest evil of the 20th century.
Thanks to the push back over the use of that tactic (basically, the users lose all credibility), desperate debaters started searching for another over-the-top analogy to use, one that hadn't developed the rhetorical baggage of the "Nazi" analogy.
Apparently, they have found one.
America's "Peculiar Institution", slavery.
...Sometimes it's Republican women in Oklahoma equating the social safety net to the ropes used in lynchings...
...Sometimes it's Sarah Palin comparing deficit spending and the national debt to slavery...
...Sometimes it's Ben Carson expounding his position that Obamacare is the worst thing since slavery...
...Sometimes it's Rand Paul likening a Supreme Court decision upholding the constitutionality of Obamacare to pro-slavery decisions of previous courts, such as in the Dred Scott case...
...Or maybe even sometimes it's someone like Trent Franks declaring that African-Americans were better off being slaves than living in modern society...
There are many examples, too numerous to list them all here, but the latest example shows that the trend is continuing unabated.
Cathi Herrod of the Center for Arizona
From her press release -
...Children are not commodities to be bought and sold – like the slave trade.
Yes, they went there. They even put it in the headline -
They (meaning CA