Britain and International Security

If we have a Daesh terrorist plotting murders in the United Kingdom, we arrest them, prosecute them, and put them in prison. If that same terrorist goes to Iraq, we try to hunt them down and kill them and blow up the building they are living in. How does that help create a rule of law or democratic pressures in Iraq? Is not the most important thing to try to impose a rule of law and diplomacy and work away to get some solution?