The phrase "This conclusion" refers to his notion that North Vietnam was inhabited by human beings. Since that is perfectly obvious it is also perfectly obvious that that is not really what he means in the first place. He challenges the reader to figure out what he means.
The term print journalism refers to reporters who work for newspapers and magazines, while broadcast journalism refers to reporters who work in television or radio. The term television journalism (as used here) refers specifically to reporters who work in television.
He answers charges that he lacks objectivity with the statement that in some circumstances objectivity is impossible.