Inaba said:
Having said that, I believe that everyone has the right to pursue happiness and to be happy, so long as that doesn't conflict with the same rights of other people. I'm inclined to think that most of society agrees with me, as shown by our attitudes towards drunk drivers and quarantines. Society tries to stop drunk drivers before they hit someone because they pose an unacceptably high risk of causing harm to others. Similarly, our society is perfectly willing to quarantine people with dangerous and highly infectious diseases in order to prevent them from spreading those diseases. Evidently, our society does not consider the happiness of any one single individual to be absolutely inalienable because no sane society of similar scale could do that and hope to survive.
And of course our society have decided to kill everybody who has the potential to drink and drive, kill everybody who has the potential to spread dangerous disease, and so on.
Oh wait no we don't.
It's not a matter of you can never deny someone happiness no matter what, obviously that'll lead to severe complications, but just as well that's not what wanted.
But there's a severe problem when potential is translated to actual by, in the words of awesome people of this thread, "butthurt fanboy logic", so as to indict a person who hasn't actually done what they're accused of doing and so execute them base on that.
Ignoring the whole question about capital punishment, it's still true that killing someone based on just things they could possibly do ain't right.
Now, if they pose a certain risk, then a good argument can be made for quarantining them, just as in the case of contagious disease. In the case of drunk drivers, once they've demonstrated a certain amount of risk, the state can and does revoke their license to drive.
In either case, however, we don't just kill them, because death is permanent and not to be taken lightly.
Applying this to Sakura, what Rin reasoned was that Sakura exceeded a certain amount of risk that necessitated her death. Even supposing a utilitarian morality,
this specific aspect is subjective, on what constitutes the baseline for receiving death instead of quarantine or other means less permanent, and so essentially refutes the entire premise that the decision is both logical and objective.
The situation does not neatly collapse into a trolley cart scenario typical of the classic utilitarian argument, and in fact, life rarely does.