At the beginning of the quotation that opens chapter 10 of Chains, Henry Knox appears to be lavishing generous praise on the people of New York. He pays a handsome tribute to them, calling them "magnificent"; he says that their house furniture is "fine."
But it soon becomes clear that Knox is damning New Yorkers with faint praise. For he then goes on to criticize them for their pride and conceit, which he regards as inimitable—that is to say, impossible to imitate. Not only that, but New Yorkers are intolerable in their profaneness. Note the high moral tone here.
But what Knox really hates about New Yorkers most of all is their lack of principle—which is prevalent—and their Toryism, which is insufferable. What Knox means by Toryism is a pro-British attitude, the kind displayed by self-described Loyalists who stood by the Crown during the Revolutionary War.
Knox is a Patriot colonel, which means he's on the opposing side to most New Yorkers in the conflict. That accounts for his dismissive and contemptuous attitude to the people of New York. As far as Colonel Knox is concerned, they are little better than traitors for supporting the British. He therefore feels perfectly entitled to describe them in such a harsh, withering tone.