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 AquinasBehold our refutation of the error. It is not based on documents of faith, but on the reasons and statements of the philosophers themselves. If then anyone there be who, boastfully taking pride in his supposed wisdom, wishes to challenge what we have written, let him not do it in some corner nor before children who are powerless to decide on such difficult matters. Let him reply openly if he dare. He shall find me there confronting him, and not only my negligible self, but many another whose study is truth.
Thomas Aquinas