The beginning of the article was somewhat confusing but I started to understand what it was all about.  I believe the author is saying that some people take grammatical errors more seriously than they should.  When people say certain words are atrocities, he believes that saying that is going overboard.  He brings up how a physical injury or an insult is much worse than any misuse of a word.  He frequently criticizes a writer, Zinsser, for his views on grammar.  Zinsser is so fanatical about grammar, he doesn't think that impact is a verb.