But doing something illegal isn't quite the same thing as terrorism, otherwise most of us would be classed as terrorists before we were through this life.

That's not meant as a glib comment. The point is, if they excluded all the people with lawbreaking pasts and terrorist connections or involvement from political life in Northern Ireland they'd be excluding the very people who have to be included if there's going to be a chance of getting anywhere at all. The corollary of this is that they have to be doing their best to try to keep the ceasefire holding.   

And is there a political party that seeks to "excuse" what happened on September 11th?