Why was Judaism so ruthless as a religion?

Answer 1

The Torah gives authority to the Sanhedrin (Jewish court) to punish certain types of crimes. They are bound by careful procedure, they must have two witnesses, and the perpetrator must be warned before he sins; otherwise he is not punished by the Sanhedrin. Also, the Sanhedrin is enjoined to make a concerted effort to seek evidence that could exonerate the defendant. This means that they must be balanced and circumspect, no matter what the crime. Their role is not intended to be one of vengeance.
Shortly before the destruction of the Second Temple, the Sanhedrin ceased dealing with capital cases, because the increased persecutions of the Romans, and the onset of the present Exile, made it impossible to fully maintain the level of scholarship and expertise needed for the Torah-procedures of the Sanhedrin. Since then, the power of Jewish courts has been greatly diminished and is now limited to imposing fines, if anything.

Killing the Canaanites:

God promised Israel (Canaan) to the Israelites(Genesis ch.28, Exodus ch.3), and commanded them to take the land (Deuteronomy ch.1 and many other passages). One major reason was because of the Canaanites' egregious wickedness, which included bestiality, incest (Leviticus ch.18), sorcery (Deuteronomy ch.18), temple-prostitution, human sacrifice (ibid.) and idolatry. God predicted that if the Israelites were lax in the fulfillment of the command, they would stray after the Canaanite gods (Numbers 33:55), and that is what came to pass.

Note:

1) Israel (Canaan) originally belonged to the Semites (after the Flood) and was gradually seized from them by the Canaanites (Rashi commentary, Genesis 12:6). This was one of the reasons why God gave the land to Abraham and his descendants (Genesis ch.13), since he was a Semite (Genesis ch.11).2) The Israelites did not simply slaughter the Canaanites. They fought them in proper battle (Joshua ch.10) with miraculous assistance from God (Exodus ch.23).
3) They warned the Canaanites concerning God's command to take Canaan (Jerusalem Talmud, Shevi'it 6:1), and gave them a chance to leave the land (ibid). The Girgashites took the warning seriously and departed to Africa (ibid.), while the Gibeonites made a treaty with the Israelites (Joshua ch.9). The rest of the Canaanites insisted on fighting, and attacked the Israelites with a massive army (Joshua ch.11).
4) Whenever fighting, the Israelites never completely surrounded any town. They offered conditional peace, and then (if peace was rejected) left one area open for escape so that whoever wanted to flee could do so (Maimonides, Mishneh Torah, Laws of kings and war ch.6).

5) The fact that the Israelites killed Canaanites need not bother you. Since secular writers claim that the evidence of Joshua's conquest comes from the Hebrew records exclusively, they must, logically, accept the Hebrew records in full, which clearly state that this was done at God's command, and give the reason too (Numbers 33:55). Even the Canaanites were impressed (Joshua 9:3-10, and 6:27).See also:

The reliability of the Hebrew record