Terrorists in general will intend to "spoil the peace and security" of others because their own security is in question. Think about when the Zionist group Irgun bombed the King David hotel in 1946 - they did it to terrorize the British, to make them leave so the formation of the state of Israel could happen faster. Israelis had no security thus, those around them lost their security as well.
It is the same thing in Afghanistan or Iraq, those people lost any security they had when the U.S. empirial army marched in. Them losing their security/stability results in our own security being at stake. Another great example is Chechnya: Russia tries to subdue the Chechyan people and in turn it losses its own security and compromises the safety of its population.
The people whom you may think of as terrorists are indeed "freedom fighters' for their own people.
"The truth is rarely pure and never simple" - Oscar Wilde