I try hard to be a Christian, because I like Christ and his teachings, but I think the Old Testament is terrible. The OT is so full of killing and suffering at God's hands, that it is hard to understand how he can be considered loving when he solves so many problems through warfare. Christ on the other hand, preached love and kindness, but it's hard for me to believe any of it because he based all of his teachings on the OT.
I'm sorry you're having trouble with this. I don't want to drive you farther away, but it will serve no good purpose to sugar-coat the things you find troublesome.
I'm going to post a few of the verses in the OT that are very cruel, and I would like for anyone to tell me what they think of them, and explain how they line up with the teachings of Christ. I ask this not to debate, but to understand.
Deuteronomy 13
6 If your very own brother, or your son or daughter, or the wife you love, or your closest friend secretly entices you, saying, "Let us go and worship other gods" (gods that neither you nor your fathers have known, 7 gods of the peoples around you, whether near or far, from one end of the land to the other), 8 do not yield to him or listen to him. Show him no pity. Do not spare him or shield him. 9 You must certainly put him to death. Your hand must be the first in putting him to death, and then the hands of all the people. 10 Stone him to death, because he tried to turn you away from the LORD your God, who brought you out of Egypt, out of the land of slavery. 11 Then all Israel will hear and be afraid, and no one among you will do such an evil thing again.
I don't have a specific explanation for that, but I'll note some family-unfriendly words of Christ Himself:
(Mat 12:46) While He was still speaking to the crowds, behold, His mother and brothers were standing outside, seeking to speak to Him.
(Mat 12:47) Someone said to Him, "Behold, Your mother and Your brothers are standing outside seeking to speak to You."
(Mat 12:48) But Jesus answered the one who was telling Him and said, "Who is My mother and who are My brothers?"
(Mat 12:49) And stretching out His hand toward His disciples, He said, "Behold My mother and My brothers!
(Mat 12:50) "For whoever does the will of My Father who is in heaven, he is My brother and sister and mother."
(Mat 10:34) "Do not think that I came to bring peace on the earth; I did not come to bring peace, but a sword.
(Mat 10:35) "For I came to SET A MAN AGAINST HIS FATHER, AND A DAUGHTER AGAINST HER MOTHER, AND A DAUGHTER-IN-LAW AGAINST HER MOTHER-IN-LAW;
(Mat 10:36) and A MAN'S ENEMIES WILL BE THE MEMBERS OF HIS HOUSEHOLD.
(Mat 10:37) "He who loves father or mother more than Me is not worthy of Me; and he who loves son or daughter more than Me is not worthy of Me.
Deuteronomy 20
16 However, in the cities of the nations the LORD your God is giving you as an inheritance, do not leave alive anything that breathes. 17 Completely destroy themthe Hittites, Amorites, Canaanites, Perizzites, Hivites and Jebusitesas the LORD your God has commanded you. 18 Otherwise, they will teach you to follow all the detestable things they do in worshiping their gods, and you will sin against the LORD your God.
Joshua 10
...
40 So Joshua subdued the whole region, including the hill country, the Negev, the western foothills and the mountain slopes, together with all their kings. He left no survivors. He totally destroyed all who breathed, just as the LORD, the God of Israel, had commanded.
Hosea 13
16 The people of Samaria must bear their guilt,
because they have rebelled against their God.
They will fall by the sword;
their little ones will be dashed to the ground,
their pregnant women ripped open."
Yes, those are certainly harsh.
We can surmise Jesus would not in this present age condone deadly force to advance His Kingdom, because He said His Kingdom is not of this world. OT Israel was under the Old Covenant, and living in different circumstances.
However, you noted an important point: Jesus based His teachings on the Old Testament. And in fact, He went so far as to identify Himself as the "I AM" Who issued the laws and commands in the OT. He never said, "Yeah, sorry guys. Dad and I were really cranky and did some awful things back then. We've learned a lot since those days." He clarified some things, changed some interpretations and applications, but never repudiated it. Rather, He consistently affirmed it.
Jesus said,
(Mat 11:28) Come to me, all you who are weary and burdened, and I will give you rest.
(Mat 11:29) Take my yoke on you and learn from me, because I am gentle and humble in heart, and you will find rest for your souls.
(Mat 11:30) For my yoke is easy to bear, and my load is not hard to carry."
But He also beat people with a whip for dishonoring the Temple; affirmed John the Baptist, who said (paraphrasing) that everyone would either be immersed in the fire of the Spirit or the fire of destruction; and said that those who remain opposed to Him will end up on the eternal ever-burning worm-infested garbage heap.