What does "fight them there so we don't have to fight them here" really mean?

Does it mean that if we weren't in Iraq the insurgents and terrorists would instead be here, planting IEDs on the corner of Main Street and Oak Avenue in Anytown, USA?  Does it mean they would be kidnapping Americans from their homes and broadcasting their beheadings on the Internet? 

Somehow that just doesn't seem plausible.  But even if you buy into the idea that a terrorist cell here in America is planning on planting IEDs, or kidnapping Americans from their home, how does "fight them there so we don't have to fight them here" stop that?  It does not.

But let’s face facts here:  A terrorist cell in America would not be interested in planting IEDs, or kidnapping Americans from their home.  They would be interested in inflicting as much damage as possible in one or two attacks. 

This leads directly to the second point about this “reason.”  How does "fight them there so we don't have to fight them here" stop an American-based terrorist cell from hijacking planes and crashing them into buildings, or from detonating a “dirty bomb” in the middle of an American city?  Again, it does not.

So, we’re back at the beginning: Just what does "fight them there so we don't have to fight them here" really mean?

Any ideas?  Other than an empty “talking point,” that is.