Defensive Investing (and this book) has one simple goal: achieving financial independence.
My father (and Don Vito Corleone, the Godfather) both advised their sons not to become "puppets on a string." Financial independence is relative. It is whatever amount of capital you need / will need with respect to your circumstances, values and interests to be as independent as possible of the government, Wall Street and an employer for your long run financial security. Why? Because governments have and will need to reduce social benefits such as retirement plans in the future. Wall Street exists for its own benefit, not that of investors, and your employer pension fund can either go broke or, more likely, be downgraded from a "defined benefit scheme / final salary plan" to a "defined contribution plan" (or in extreme - have to be rescued by a government pension protection plan and your benefits reduced as part of the bail-out). As things now stand you largely have to contribute your money and take your chances on the future value of stock and bond markets. Financial independence is being free of soul-destroying anxiety as you approach the end of your working life.