Sentence:  Compared with the researchers' own anxious exertions and the towering unknowns that swirled before them, Boger's calm and assiduous attention to his slides seemed to many of them—dangerously, a few argued—aloof. ¶ Boger thought to convince them otherwise was “an <WSD>unpersuadable</WSD> issue,” and so he didn't try. 
Meaning of the word marked with <WSD> tags:  Of which one cannot be persuaded.