I think I might refine the definition of the argumentum ad imperfectionem somewhat today. As I alleged the other day, ad imperfectionem fallacy occurs when one asserts that the minor errors in someone's argument may be justifiably exaggerated by opponents of that argument. So, for instance, minor errors in a legal filing undermine one's entire case, not just those particular claims relevant to those errors. For, after all, if there are a couple of typos, who knows what other kinds of serious errors there could be. This, of course, is the response of a crazy person. But not all crazy is the same, so it's worth it to take a closer look at the crazy.
On this description, the imperfectionem is a variation of the ignoratio elenchi (IE). The ignoratio elenchi, sometimes called "missing the point" or–get this–"non sequitur", is a kind of a catch-all category of fallacy: any other basic failure of informal entailment gets thrown in here. Here, for instance, is the way Patrick Hurley puts it in A Concise Introduction to Logic:
Missing the point illustrates a special form of irrelevance. This fallacy occurs when the premises of an argument support one particular conclusion, but then a different conclusion, often vaguely related to the correct conclusion, is drawn.
but in some ways it serves as a catchall for arguments that are not clear instances of one or more of the other fallacies.
Textbooks will often use examples of IEs with outrageous conclusions where more moderate ones are available. So, for instance, given the inevitable shortcomings in weather forecasts, one ought not to listen to them at all. That's dumb, as weather forecasts are predictions, and predictions can be wrong. Again, the conclusion of a crazy person. This conclusion, in that particular example, is driven by the idea that any imperfection, however minor, in the assertions of one party are sufficient to create doubt about that party's entire case.
I think the argumentum ad imperfectionem is focused on the inference from the relatively minor shortcomings of one side to either (a) the truth of the opposite side (in which case it looks like a false dichotomy) or (b) to the conclusion that no one can really claim to know one's conclusion is true (in which case it looks like an appeal to ignorance) or finally (c) to the conclusion that the opposite side is relatively more justified.
I can think of examples of all three of these. But for today, here's an example of (a):
(a) in the minds of many, the various quibbles and revisions involved in the science of global warming justify skepticism of the entire thesis. Here's an example of that from the Washington Post:
"What's happened here is that there's an industry of climate-change denialists who are trying to make it seem as though you can't trust anything that is between the covers" of the panel's report, said Jeffrey Kargel, a professor at the University of Arizona who studies glaciers. "It's really heartbreaking to see this happen, and to see that the IPCC left themselves open" to being attacked.
That's not an example of an actual argument, as it is a report of someone else's argument. But people really do make that allegation, unfortunately.
Maybe if I'm motivated I'll find examples of the others later.