Albert Guerard's writing was affected by his wartime experience (political intelligence work in France) and by the pressures and ambiguities of the subsequent Cold War. You can read more here: Albert (Joseph) Guerard Biography - Albert Guerard comments: http://biography.jrank.org/pages/4384/Guerard-Albert-Joseph.html#ixzz0imxUxsgr

I suspect that he was saying that while he is willing to exert effort to help humanity and make the world a better place, he nevertheless has limits to this effort. He would not provide help indiscriminately; he would use his "critical" thinking to evaluate people and situations to determine worthiness of his help.