First, I'd like to know the technical term for this fallacy, and then I'd like at least one down-to-earth example that I can refer to in a section heading.
Background: Down Syndrome tends to feature some cognitive impairment, but this can range from mild to moderate etc. etc. A nasty guy is arguing that Student's intellectual disability is moderate, rather than mild. However, as offensive as his insistence on that point is, it's still irrelevant, because Student still has the right to a Free, Appropriate Public Education (FAPE). (The nasty guy is suggesting that because Student's impairment is moderate, Student's IEP goals are wildly undoable. But IDEA 2004 guarantees Student the right to FAPE regardless. FAPE would still be guaranteed even if the impairment were profound. FAPE is FAPE, and IDEA is for everyone.)
I can explain it in the document I'm drafting, exactly as I explained it here, but I would also like to label it for the fallacious argument that it is. For example, another section of my draft is called
Individualization vs. Least Restrictive Environment: A False Dichotomy
That one is okay as is, because everybody and his cousin understands false dichotomy.