curious Then there will be a judgement. And if that is a death sentence, only then an order of killing that person is acceptable.
As long as not concicted by a court, presumption of innocence is the guiding principle of all western democracies.
In my view, you are mixing up two separate orders of things. One thing is the administration of justice. It is based on the law, procedural guarantees, its purpose is to prove guilt and to impose a just punishment, appropriate to the circumstances of the crime. It can be said to be the ordinary response of the state to the dangers of crime. The physical elimination of 'enemies of the state' is an entirely different matter. This is an extraordinary action, not aimed at administering justice, but only at protecting the security of the state and its society. It is used when it is obvious that ordinary police and judicial action will fail. It is based solely on political will, the state's actual capabilities (military, intelligence) and the state's general right to defend itself, rather than on specific statutory provisions.
Yes, I know that the definition of terrorism is vague and various brutal regimes love to lump their opponents into it. However, Western countries tend to be restrained enough in this regard that I do not think they would violate the rule of law with this.