But the point is that we have spent the money and the problem groups have not remotely been eliminated. That makes it a waste. They have just hopped over the border plus sprung up in a number of other places. Spending on checking who comes and goes from the UK/ monitoring those here who could be a threat etc. would seem to achieve better value without 453 personnel being dead and 2000 plus maimed and wounded.
You hunt them wherever they pop up next. Fighting these Islamic jihadists is a long term war and we're seeing that in Syria right now that leaving them to their own devices isn't an option. Pulling up the drawbridge doesn't help the rest of the world or your allies.