two sides of a coin?
The very nature of the statement "one man's..." speaks of its inherent duality. You'll probably never convince one side of the other's definition.
But, for the sake of argument, forget the extreme examples of Palestinian suicide bombers or the events of Sept. 11. Webster's dictionary defines terrorism as "use of terror or violence to intimidate, subjugate, etc., especially as a political weapon." Examples of 'terrorist' are listed as "an agent or supporter of the revolutionary tribunal during the French Revolution" or "any of certain extreme revolutionary socities in czarist Russia."
In both examples, terrorist is defined as an opponent of the status quo or ruling government. The thing to note is the political nature of terror. If you have 'politics' and you have 'opposition,' then from either side you have 'propaganda.' It's the mixing of message and meaning for political means. In other words, "one man's freedom fighter is another man's terrorist." You can argue one side or the other until you are blue in the face (Russian vs. Chechen, Contra vs. Sandinista, Chinese vs. Tibetan), but there is truth in that statement...the truth is just defined in different ways.
Such is the nature of politics and governments...and it's that which makes this absurd bantering about of the word "terrorism" on the part of the U.S. government, the British government and all such a danger.