There appears to be some sllight confusion here, though the right answer is there.
You were right in your original post - I believe "whose aversion" is the subject and "are" the verb of the sentence but it appears to me that the verb should be "is" because the subject is singular", as charliedeut confirmed in post #2, parser in post #4 and riquecohen in post #5. Your friend (post #6) made the same mistake as the writer of the original writer.
fivejedjon and everyone who's backed my view, thanks for your support.
It really is a complicated piece of writing that even native speakers stumble over.
I'm glad I was barely on the right track.