Over 20 years ago, the great philosopher Alvin Plantinga gave us an accurate summary of the way in which the term “fundamentalist” is often deployed as a lazy slur rather than a serious argument:
We must first look into the use of this term “fundamentalist.”
On the most common contemporary academic use of the term, it is a term of abuse or disapprobation, rather like “son of a b*tch,” more exactly “sonovab*tch,” or perhaps still more exactly (at least according to those authorities who look to the Old West as normative on matters of pronunciation) “sumb*tch.”
When the term is used in this way, no definition of it is ordinarily given. (If you called someone a sumb*tch, would you feel obliged first to define the term?)
Still, there is a bit more to the meaning of “fundamentalist” (in this widely current use): it isn’t simply a term of abuse. In addition to its emotive force, it does have some cognitive content, and ordinarily denotes relatively conservative theological views. That makes it more like “stupid sumb*tch” (or maybe “fascist sumb*tch”?) than “sumb*tch” simpliciter.
It isn’t exactly like that term either, however, because its cognitive content can expand and contract on demand; its content seems to depend on who is using it. . . .
The explanation is that the term has a certain indexical element: its cognitive content is given by the phrase “considerably to the right, theologically speaking, of me and my enlightened friends.”
The full meaning of the term, therefore (in this use), can be given by something like “stupid sumb*tch whose theological opinions are considerably to the right of mine.”
—Alvin Plantinga, Warranted Christian Belief (Oxford: 2000), 245.