Personnally, I don't give a s*** about wether the terrorist came from Western Europe or anywhere else, nor what brand of religon they do their killing under. A murdering terrorist is a murdering terrorist. Full stop.
Having said that, consider the old phrase, "One man's terrorist is another man's freedom fighter."
Just suppose for a moment that the allies had lost World War Two. The whole of Europe in 2004 is under Nazi rule. How many of you might be prepared to join a criminal organisation to try and free ourselves from it? Does a bomb in a crowded pub full of officers of the occupation (but also with inocent bystanders) sound so unreasonable now? Well, does it?