Who's complaining? I actually don't have a problem at all with the slaughter of the Canaanites from a judgment standpoint. They were abhorrent idolaters and child sacrificers in the worst possible ways imaginable; killing the children saved the from growing up in such a culture, if you want to look for a bright side. God is unchanging in his character and his ways.Therefore this begs the question of why He wanted the Israelites to wipe out the ungodly nations but does not expect Christians to do the same. Now, this is something of a rhetorical question obviously. But on the one hand we have "wipe out your enemies" and on the other we have "love your enemies."
HI Todd: My take on this is derived from a sermon by Major Ian Thomas who I believer gives us and excellent understanding of this situation with the Canaanites'. Simply put, the C's represent the flesh, the carnal, sinful nature...they are descendent from Esau and Edom whom God swore he would war against forever. So, in this life, our sinful nature is to be "put to death", crucified, Mortified etc and we are to live according to Christ who lives in us. But, we all know that the sinful nature erupts from time to time, situation or circumstances arise that bring forth our carnal nature where we didn't realize it was holding a piece of land that now must be taken for Christ. This continual battle that Israel faced is our battle today and it does us well to understand that their defeats teach us where to be watchful, their victories teach us what God will do when we die to self. Hope this sheds some light. Check out Major Ian Thomas's sermons dealing with going into the promised Land. He can preach it of far better than I can.