I have a deficiency in my ability to stand for more than several minutes. I am not insulted to hear that I have a deficiency, living that reality is far more insulting.
Lets assume I am invited to a professional event, one where I know the location and layout. If the event organiser has deliberately removed all the seating because it didn't match their cocktail party aesthetic, is the deficiency in my ability to stand or their ability to plan for the completely predictable outcome that all their attendees might not be able to or want to stand for a full 5 hour event?
And even if you think the deficiency is my problem to solve alone (which it legally is not), why does having a deficiency also then imply that I as a person am deficient? My ability to stand does not define my existence, so why has my personhood been defined as deficient? That's the insulting part. My standing time deficiency doesn't even limit my existence if a couple of chairs also exist nearby. These are not a new or expensive or niche technology.