It makes reference to the power of the media. If you use a sword to attack an enemy, only you and he will know of his transgressions and the reasons that you attacked him. But if you manage to relate your enemy's faults to the news media, it will get printed in the newspapers and on television. He will be universally shunned and reviled.
Likewise, on a larger scale, a person can make his message heard more effectively by using the media rather than via violence. He will garner more support by carefully spelling out his views in the press rather than by staging violent events (such as bombings).