Sentence:  I speak of `` the largest possible measure '' because any person who supposes that these conditions can be universally and perfectly achieved - ever - reckons without the inherent imperfectability of himself and his fellow human beings , and <WSD>is</WSD> therefore a dangerous man to have around . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)