Because you can tell the difference between pouring water on a towel held over the mouth of three separate individuals (and under very carefully controlled conditions), and sending 17 million people to the gas chamber*.
(H/T: Melissa Clouthier)
But, do you know something? Don't get mad.
*For the record: this comment does not mean that I deny you your right to disapprove of the former. Merely that Dodd's equation of it with the latter neatly shows why we have Godwin's Law in the first place.
Crossposted to Moe Lane.