Arguments about whiskey often start, tragically, before anyone has even had a drink. They argue about how to spell it ('whisky' or 'whiskey') and even what it means.
There are a few people who consider 'whiskey' and 'alcohol' to be synonymous, especially when discussing the history of distilled spirits, and to the extent that distilled spirits were almost universally called 'water of life' at first, the different names had more to do with local language than with the type of fermentable substrate used.
The word 'whiskey' is derived from the phrase 'water of life' in Gaelic.
When, however, people began to distinguish between types of aqua vitae, they did so by raw material. That may have been coincidence, but nevertheless 'brandy' came to mean distilled wine and 'whiskey' came to mean distilled beer, and that divide occurred in Europe maybe 500 years ago. 'Rum,' to mean a spirit made from sugar cane, came later.
In all cases, if someone in, say, the West Indies happened to make some spirit from, say, wheat, they might very well call it 'rum,' that term being understood to mean distilled spirit. This is common in the literature, someone writing in the 17th century might mention, "a rum made from wheat."
In context, it's not so much wrong as it is imprecise.
In India today, because of the British colonial influence, they call their local spirit 'whiskey' even though it is made from sugar cane. They even flavor it so it tastes vaguely like scotch. They are unmoved by Western insistence that whiskey must be made from grain and are unwilling to call their whiskey rum.
They have agreed not to call it scotch.
Indian distillers also make what we would consider proper whiskeys, from grain.
Colonialism aside, there is a long tradition of 'whiskey' being largely synonymous with 'distilled spirit' in beer-making cultures. 'Brandy' has been used the same way in wine-making cultures.
The idea that whiskey and brandy must be aged is of fairly recent vintage, about a century and a half, but it has become widely accepted in custom and law.
The fundamental rationale behind regulating the labeling of distilled spirits is that a person shouldn't have to take a course to buy a drink. Fundamentally, when a consumer orders 'whiskey,' he or she should have a pretty good idea what to expect and a pretty good chance of having that expectation realized. So, first and foremost, whiskey should look, taste, and function like whiskey.
The narrower categories such as 'scotch whiskey' or 'bourbon whiskey' branch out from there.
That's pretty much how things are. We're generally well served. But increasing globalization makes it increasingly complicated.
The solution favored by the largest drinks companies is to forget types and focus on brands. That's why Jeremiah Weed (a Diageo product) can be a whiskey, a vodka, a liqueur, and a beer (i.e., flavored malt beverage).