I've always considered Godwin's assertion to be nonsense.
In the NAZIs and Hitler we have one of the greatest teaching events of all time. The number of useful analogies, life lessons, and historical warnings that can be taken from that series of events is immense.
Godwin's assertion is based on the premise that no other event or decision can be compared in any way to NAZIs/Hitler, so there is nothing to learn from such comparisons. The truth is that the motivations and actions weren't all that unique, just clarifying by their extreme nature. With over 40 million people killed, less than 100 years ago, I would hope that we could at least be open to learning something from it.