Without doubt one is allowed to resist against the unjust aggressor to one's life, one's goods or one's physical integrity; sometimes, even 'til the aggressor's death... In fact, this act is aimed at preserving one's life or one's goods and to make the aggressor powerless. Thus, it is a good act, which is the right of the victim.
Thomas AquinasIt would seem that the ingratitude, whereby a subsequent sin causes the return of sins previously forgiven, is a special sin. For, the giving of thanks belongs to counter passion, which is a necessary condition of justice. But justice is a special virtue. Therefore this ingratitude is a special sin. Thanksgiving is a special virtue. But ingratitude is opposed to thanksgiving. Therefore ingratitude is a special sin.
Thomas Aquinas