Shalom Althea,
It sounds as if your friend is a Marcionist or at least unknowingly subscribing to the doctrine of Marcion. Marcion preached that the "God of the Old Testament" was cruel and evil while Jesus, the "God of the New Testament" was loving. He was of course eventually rejected as a heretic but his teachings have permeated Christianity ever since. YHWH is the same today, yesterday, and forever more, the Elohim that ordered the absolute execution of the inhabitants of the land of Canaan is the same Elohim that put His words in Yeshua's mouth at the sermon on the mount. What Yeshua was teaching was how to behave peacably in a community, not how to treat all persons. If someone is attempting to kill you or one of your children, you absolutely have the right to defend yourself. In the Tanakh, YHWH allowed His people to stay longer in Egypt because the iniquity of the peoples of Canaan was not yet complete. Only after their actions had become an absolute abomination did Elohim send His armies (Yisrael) against the peoples of that land. The Amelekites were also ordered to be erradicated because they were a band of roving marauders that kept attacking the camp.
If you need some verses to show that Yeshua wasn't this pacifist that Christianity portrays Him as, here you go:
Matthew:10:34-37
“Do not think that I have come to bring peace on earth. I did not come to bring peace but a sword, for I have come to bring division, a man against his father, a daughter against her mother, and a daughter-in-law against her mother-in-law – and a man’s enemies are those of his own household. “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
Luke 22:36-38
And He said to them, “But now, let him who has a purse take it, likewise also a bag. And let him who has no sword sell his garment and buy one. “For I say to you that what has been written has yet to be accomplished in Me, ‘And He was reckoned with lawless ones.’ For that which refers to Me has an end too.” And they said, “Master, look, here are two swords.” But He said to them, “That is enough”
Then of course there is Revelation 1:16, 2:12, 2:16, 19:15, 19:21 which describe the double-edged sword that comes from Yeshua's mouth when He returns to judge and make war (Rev 19:11).
What Yeshua was preaching on the mount was how to love your neighbor as yourself (Lev 19:18). The Pharisees at the time had taught that "neighbor" only meant people of your own nationality and religion. Thus in the parable of the Samaritan, Yeshua was showing that one's neighbor extended to anyone arount them, not just people of the same nationality and religion (the injured Jewish man would have hate the Samaritan, and yet the Samaritan showed compassion over one who professed to be his enemy). Yeshua certainly did not say that if your enemy rapes your daughter that you should offer them your other daughter. The context is within civilization, not those who come with evil intent.
I hope that makes sense, I'm kind of all over the place with my thoughts today.
Shalom,
Ryan