Sentence:  The “even be killed” is not comic, for Thoreau the individualist must have found it in theory as difficult to imagine himself dying for others as Thoreau the <WSD>abhorrer</WSD> of violence found it difficult to imagine himself killing another individual. 
Meaning of the word marked with <WSD> tags:  One who abhors. (Early 17th century.)<ref name=SOED>(page=4)</ref>