I would say the "why not" comes down not to why not dispute it but why dispute it in the way it was done, by insulting Inman for being from the west coast, for

I would say the "why not" comes down not to why not dispute it but why dispute it in the way it was done, by insulting Inman for being from the west coast, for being young, for being unhappy, etc. Rather than insult him for perpetuating untruths, the author instead tosses out weird demographic and geographic insults. It reminds me of the saying attributed to Eleanor Roosevelt, "Smart people talk about ideas. Mediocre people talk about things or events. Stupid people talk about people." Speaking about specific people denigrates a conversation. A discussion will always be more interesting and enlightening and overall useful if instead aimed at ideas or even slightly abstracted.