That seems like an extraordinarily hasty generalization. What you seem to be saying is that most non-fundamentalist religious people won't agree to even a common-sense definition of truth; I'm very skeptical of this claim. Have you tried using really really simple examples, like "snow is white"?
You are right. It is a hasty generalization, hence the word 'tend'. When handled with care, these can be useful.
Based on the community's continuing interests in diet and religion, I'd like to point out this blog post by the coauthor of Protein Power, Michael Eades, wherein he suggests that biblical literalism tends toward a low-fat approach to nutrition over a low-carb philosophy, by essentially throwing out a bunch of evidence on the matter:
While there's a clear persuasive agenda here and I won't present a full analysis of the situation, Eades also mentions biasing use of language earlier in the article. In particular, beware applause lights and confirmation bias in evaluating.