Calling someone out for invoking Goodwin's rule is legitimate because there is such an emotionally charged fear/hatred programmed into Western culture about Hitler and his actions that using it to shoot down an argument is an unreasonable extrapolation.
After the American Civil War, Northern politicians were infamous for "waving the bloody shirt" to shoot down Southern politicians in Senate. That is, they'd throw the blame on the South again and again because they had seceeded from the Union as the Confederacy. Whether secession was 'right' or 'wrong' is immaterial, merely using the fact that the South tried something, screwed up, and was defeated doesn't automatically void any other argument they make from then on, and you can't just compare everything to slavery and confederacy.
That's like the Christian fundamentalist saying "God said it so it must be true." That technically ends the argument, because, in their eyes, who are you to argue with God? Who are we, likewise in your eyes, to argue with Western civilization?
To sum it up, comparing something to Hitler's practices in a rational argument is as fair a move as punching somebody in the balls during a boxing match. Yes, it's a powerful blow, but it's considered pretty underhanded.
After the American Civil War, Northern politicians were infamous for "waving the bloody shirt" to shoot down Southern politicians in Senate. That is, they'd throw the blame on the South again and again because they had seceeded from the Union as the Confederacy. Whether secession was 'right' or 'wrong' is immaterial, merely using the fact that the South tried something, screwed up, and was defeated doesn't automatically void any other argument they make from then on, and you can't just compare everything to slavery and confederacy.
That's like the Christian fundamentalist saying "God said it so it must be true." That technically ends the argument, because, in their eyes, who are you to argue with God? Who are we, likewise in your eyes, to argue with Western civilization?
To sum it up, comparing something to Hitler's practices in a rational argument is as fair a move as punching somebody in the balls during a boxing match. Yes, it's a powerful blow, but it's considered pretty underhanded.