Many people today, Christian & non-Christian alike, read about the God of the Old Testament and say, 'that can't be the same God of the New Testament!' ( in other words, even ), and some even suggest something as ridiculous as the Son of God ( Jesus ) toned His Father down a bit when He came onto the Scene!
Apparently the God of the New Testament is a kinder, gentler God than the God of the Old Testament was!
Okay, so the commands given to the Children of Israel concerning the Canaanites WERE pretty harsh; did Yahweh really command His People not to commit murder ( 7th commandment ), then command them to commit genocide on the inhabitants of the Land to which He led them?! It would certainly seem so! A closer and more sensible look, though, might help us to understand why our Gracious & Merciful God might command or even witness such a thing.
First off, we should ask ourselves, 'why would a just God order such genocide?' Well, the key here is the word 'just'. Scripture is full of references to how ungodly the nations were whom the Israelites were commanded to blot out from under heaven. Because Yahweh IS a just God, He was entirely in the right to order the extinction of these people!
At this juncture, you will likely hear arguments like 'how could a just God require obedience from a people to whom He had not given His Law?' I mean, the apostle Paul wrote to the Roman Christians that 'where there is no law [ there is ] no transgression' ( Romans 4:15 ). So, if they had no Law, then how could their genocide be justified? The simple answer, of course, is that they DID have the Law! Quoting the apostle Paul again, in Romans 2:14, we see that 'when Gentiles, who do not have the law, by nature do the things in the law, these, although not having the law, are a law to themselves'. This is further cleared up when we back up a bit to the first part of Paul's statement, in verse 12; 'For as many as have sinned without law will also perish without law'.
Obviously, the Law of Nature has been in existence since Nature itself has been in existence! By nature, without having to be told, people know when something 'just ain't right'. Now, granted, the nations around Israel were not expressly given Yahweh's Law, like Israel was, but they knew that certain things, bestiality & homosexuality, just weren't the way things work! It was because of the transgression of this Natural Law that the Caananites were to be exterminated, or banished from the Land!
Another reason that Yahweh ordered His Children so is that He wanted them to remain pure & holy to Him ( think of the modern wedding vow-'keep thee only unto him/her' ), and by ridding the Land of Caananite influence, the Israelites should have remained thus to their God! This obviously did not work out, on the whole, to that end, although it could well be argued that this was not the End promised in the first place!