Because all it takes is for one goof to ruin the reliability of your entire PR campaign and make you a laughingstock. Obviously, your job is to achieve the client's objectives, and that includes making the best case for the client's point of view. You are not expected to provide full coverage of opposing points of view. But this does not mean that you should rely only on research resources promoting your cause. This will not only give you more Key Ideas, it will also help shape your Angle and, therefore, your Message.
Good research is especially important in today's media environment.
There is more and more information out there, and more and more advocates spinning the news. That can be confusing. When you establish trust with editors and reporters, you will rise above your competitors in stature and respect. This type of public relations research is discussed beginning on page 72 of your text. This assignment is an entirely separate subject from market research, which is so important to PR planning and writing.