There is a danger of extrapolating from one's data to the world at large. This error is not unknown in quantitative research, of course. It may be avoided by explicitly survey-oriented studies, but is not uncommon in experimental social psychology when findings are subtly generalised from the sample of the experiment (say, a set of North American undergraduates) to the universal categories they are supposed to represent (women, high achievers, people with a certain attributional style). Discussion sections of experimental papers sometimes use such unqualified terms, with the logical implication that they encompass all members of that category.
The same danger of False Survey lurks for qualitative work that discovers that certain respondents use certain discourses or ways of speaking. It is fatally easy to slip into treating one's findings as if they were true of all members of the category in which one has cast one's respondents. For example, an analyst reading our interview extract might see, in the respondent's way of talking, a 'traditionalist discourse of marriage'. They might then be tempted to attribute that discourse to all people in his position ('non-University-educated young women', if that was the demographic information supplied along with the extract). This attribution might be done explicitly, but is still more likely to happen unconsciously, in the way the writer uses demographic categories to refer to the people in their data.
Probably few discourse analysts want or intend explicitly to be reporting surveys; but without care, their reports may give that impression. Such a fault makes the work an easy target for the quantitatively-minded, who will properly see it as failing to supply appropriate evidence for its claims. If a survey is wanted, survey tools must be used.