We cannot easily go against the natural law of self preservation. The Catechism teaches us that "one is bound to take more care of one's own life than of another's."
2264 Love toward oneself remains a fundamental principle of morality. Therefore it is legitimate to insist on respect for one's own right to life. Someone who defends his life is not guilty of murder even if he is forced to deal his aggressor a lethal blow... Nor is it necessary for salvation that a man omit the act of moderate self-defense to avoid killing the other man, since one is bound to take more care of one's own life than of another's.
Jesus did not literally give the other cheek:
"And when he had said these things, one of the servants standing by gave Jesus a blow, saying: 'Answerest thou the high priest so?' Jesus answered him: 'If I have spoken evil, give testimony of the evil; but if well, why strikest thou me?'" (John 18:22-23).
Neither did St. Paul:
"And the high priest, Ananias, commanded them that stood by him to strike him on the mouth. Then Paul said to him: 'God shall strike thee, thou whited wall. For, sittest thou to judge me according to the law and, contrary to the law, commandest me to be struck?'" (Acts 23:2-3).
The Doctors of the Church explained this to us:
As, when we read in the Gospel, "Thou hast received a blow in the face, make ready the other cheek." Now as an example of patience can none be found than that of the Lord Himself more potent and excellent; but He, when smitten on the cheek, said not, Behold here is the other cheek, but He said, "If I have spoken ill, bear witness of the evil; but if well, why smitest thou Me?"Where He shows that the preparation of the other cheek is to be done in the heart. Which also the Apostle Paul knew. for he, too, when he was smitten on the face before the high priest, did not say, Smite the other cheek: but, "God," saith he, "shall smite thee, thou whited wall: and sittest thou to judge me according to law, and contrary to law commandest me to be smitten?" ~ St. Augustine, On Lying
I answer that, Just as we need patience in things done against us, so do we need it in those said against us. Now the precepts of patience in those things done against us refer to the preparedness of the mind, according to Augustine's (De Sermone Domini in Monte i,19) exposition on our Lord's precept, "If one strike thee on thy right cheek, turn to him also the other": that is to say, a man ought to be prepared to do so if necessary. But he is not always bound to do this actually: since not even did our Lord do so, for when He received a blow, He said: "Why strikest thou Me?" (John 18:23). Consequently the same applies to the reviling words that are said against us. For we are bound to hold our minds prepared to submit to be reviled, if it should be expedient. Nevertheless it sometimes behooves us to withstand against being reviled, and this chiefly for two reasons. First, for the good of the reviler; namely, that his daring may be checked, and that he may not repeat the attempt, according to Proverbs 26:5, "Answer a fool according to his folly, lest he imagine himself to be wise." Secondly, for the good of many who would be prevented from progressing in virtue on account of our being reviled. Hence Gregory says (Hom. 9 super Ezech.): "Those who are so placed that their life should be an example to others, ought, if possible, to silence their detractors, lest their preaching be not heard by those who could have heard it, and they continue their evil conduct through contempt of a good life." ~ St. Thomas Aquinas, Summa Theologica, "Treatise on the Cardinal Virtues" Q72, A3
