It does seem harsh. Let's paint a clear picture. The Christians were in the minority. The constitutional law of the land was the Law of Moses. The king men had conspired and combined to overthrow Pahorah and succeeded and had sent the Lamanites a letter. In this letter, they declared that they had taken control and desired an alliance to rule and to squash Christianity. Captain Moroni did not seek war abroad. War had come to his front door.
Alma 48:14 Now the Nephites were taught to defend themselves against their enemies, even to the shedding of blood if it were necessary; yea, and they were also taught never to give an offense, yea, and never to raise the sword except it were against an enemy, except it were to preserve their lives.
15 And this was their faith, that by so doing God would prosper them in the land, or in other words, if they were faithful in keeping the commandments of God that he would prosper them in the land; yea, warn them to flee, or to prepare for war, according to their danger;
16 And also, that God would make it known unto them whither they should go to defend themselves against their enemies, and by so doing, the Lord would deliver them; and this was the faith of Moroni, and his heart did glory in it; not in the shedding of blood but in doing good, in preserving his people, yea, in keeping the commandments of God, yea, and resisting iniquity.
Moroni did not go to war without first obtaining authority from God to do so, which he explained to Pahoran in his epistle.
34 And now behold, I, Moroni, am constrained, according to the covenant which I have made to keep the commandments of my God
to which Pahoran replied graciously:
19 And now, Moroni, I do joy in receiving your epistle, for I was somewhat worried concerning what we should do, whether it should be just in us to go against our brethren.
20 But ye have said, except they repent the Lord hath commanded you that ye should go against them.
Amaleckiah and his brother Ammoron wanted to rule not only the Lamanites, but all the Nephites as well. They were systematically taking control wherever they went.
The Lord gave a law to His people, even the ancients and also to Nephi:
D&C 98:11 And I give unto you a commandment, that ye shall forsake all evil and cleave unto all good, that ye shall live by every word which proceedeth forth out of the mouth of God.
12 For he will give unto the faithful line upon line, precept upon precept; and I will try you and prove you herewith.
13 And whoso layeth down his life in my cause, for my name’s sake, shall find it again, even life eternal.
14 Therefore, be not afraid of your enemies, for I have decreed in my heart, saith the Lord, that I will prove you in all things, whether you will abide in my covenant, even unto death, that you may be found worthy.
15 For if ye will not abide in my covenant ye are not worthy of me.
16 Therefore, renounce war and proclaim peace, and seek diligently to turn the hearts of the children to their fathers, and the hearts of the fathers to the children...
23 Now, I speak unto you concerning your families—if men will smite you, or your families, once, and ye bear it patiently and revile not against them, neither seek revenge, ye shall be rewarded;
24 But if ye bear it not patiently, it shall be accounted unto you as being meted out as a just measure unto you.
25 And again, if your enemy shall smite you the second time, and you revile not against your enemy, and bear it patiently, your reward shall be an hundred-fold.
26 And again, if he shall smite you the third time, and ye bear it patiently, your reward shall be doubled unto you four-fold;
27 And these three testimonies shall stand against your enemy if he repent not, and shall not be blotted out.
28 And now, verily I say unto you, if that enemy shall escape my vengeance, that he be not brought into judgment before me, then ye shall see to it that ye warn him in my name, that he come no more upon you, neither upon your family, even your children’s children unto the third and fourth generation.
29 And then, if he shall come upon you or your children, or your children’s children unto the third and fourth generation, I have delivered thine enemy into thine hands;
30 And then if thou wilt spare him, thou shalt be rewarded for thy righteousness; and also thy children and thy children’s children unto the third and fourth generation.
31 Nevertheless, thine enemy is in thine hands; and if thou rewardest him according to his works thou art justified; if he has sought thy life, and thy life is endangered by him, thine enemy is in thine hands and thou art justified.
32 Behold, this is the law I gave unto my servant Nephi, and thy fathers, Joseph, and Jacob, and Isaac, and Abraham, and all mine ancient prophets and apostles...
The Lord commanded us to turn the other cheek. But He also gave provisions whereby His people are justified in defending themselves if they want to be preserved to fulfill His commandments. Yes, the Nephites could have all prostrated themselves as the Anti-Nephi-Lehis did and obtained a greater reward. That would have cut short the purposes of the Lord concerning Lehi's seed, though. And if the Lord's people obey God precisely, then He will fight the battles for His people. Should not the bridegroom defend his bride, Zion, if she is worthy? Indeed the Lord preserved the Nephites until they were ripe for destruction. But at this stage in the game, they were not. Quite the contrary:
Alma 46:15 And those who did belong to the church were faithful; yea, all those who were true believers in Christ took upon them, gladly, the name of Christ, or Christians as they were called, because of their belief in Christ who should come.
16 And therefore, at this time, Moroni prayed that the cause of the Christians, and the freedom of the land might be favored.
17 And it came to pass that when he had poured out his soul to God, he named all the land which was south of the land Desolation, yea, and in fine, all the land, both on the north and on the south—A chosen land, and the land of liberty.
18 And he said: Surely God shall not suffer that we, who are despised because we take upon us the name of Christ, shall be trodden down and destroyed, until we bring it upon us by our own transgressions.