Ok. How would Mill react to this (looking in utilitarianism):
Somebody trying to harm someone else, but the person that might be harm kills the other person in defense.
What would John Mill say to this?

Ok. How would Mill react to this (looking in utilitarianism):
Somebody tring to harm someone else, but the person that might be harm kills the other person in defense.
What would John Mill say to this?

I would argue that Mill would have little to say on this matter. Utilitarianism of Mill and Bentham does not deal very well with individual motives for an action. Utilitarianism tries to separate the rightness or wrongness of an action from the goodness or badness of the agent performing the action.

An action is deemed good if it promotes the greatest happiness of the greatest number. This is the principle of utility.

Consider this thought experiment.

A person may act in self defense if someone is trying to harm them or even trying to kill them. The outcome may be that the only way to defend themselves was to kill the aggressor. However a problem arises if the aggressor turned out to be someone who had found a universal cure for cancer. The cure is now lost forever. Now the person who found himself being attacked would argue that his actions were RIGHT because he was trying to save his life. Utilitarianism would argue that this actions were WRONG because this person has killed off any hope of saving millions of people people with cancer. This is because his actions did not promote the greatest happiness of the greatest number. We could even take this a step further and claim than a large number of people acting from evil motives may inadvertently or accidentally promote general happiness; so according to the principle of utility this is good.

If we wanted to be selective in quoting Mill from his,"Essay on Liberty" we could write;

'... that the sole end for which mankind is warranted, individually, or collectively, in interfering with the liberty or action of other members, is self protection'.

We could fashion an argument for self protection from this quote. In fairness to Mill he would argue that a person can do anything they wish so long as they don't harm others in the process. Harm could be physical or psychological in this context.