Self-defense.

[iwerk2hard]

Yes it would be difficult living with the fact that you took a human life.
BUT, when you know that the maggot whose life you took made an attempt to take YOUR life or the life of someone you love, it should be a lot easier to handle, especially when you know that they will no longer be a menace to society.
(Not to mention the fact that your tax dollars won't be spent providing an existence and legal defense to someone who wouldn't give you anything and was willing to take EVERYTHING you had.)