With regard to the parts of the Old Testament that record, encourage, or even command violence, a frequent response is that we should interpret them with a ‘Jesus hermeneutic’.  Trouble is, Jesus didn’t seem to find these accounts nearly so problematic as we do.

Distinguished Old Testament scholar John Goldingay (not exactly a died-in-the-wool fundamentalist) puts it like this:-

Many modern people don’t like the way the book portrays Joshua’s leading Israel in killing many Canaanites, but there is no indication that the New Testament shares this modern unease. The New Testament pictures Joshua as a great hero (see Hebrews 11) and portrays God’s violent dispossession of the Canaanites as part of the achievement of God’s purpose in salvation (see Acts 7). If there is a contradiction between loving your enemies and being peacemakers on one hand, and Joshua’s undertaking the task at God’s command, on the other, the New Testament does not see it.

We need to separate two issues in considering the questions all this raises. One is that the Old Testament sees the Canaanites as under God’s judgment for their wrongdoing. The idea that God judges people for their wrongdoing runs through both Testaments; Jesus is tougher about it as he pictures God sending people not merely to early death but to hell, where there is weeping and gnashing of teeth. In the context of modernity, we do not care for this idea, but we need to note its prominence in Jesus’ thinking.

The other issue is that the Old Testament sees God as using the Israelites as the agents of judgement. I’m not sure why we don’t like this idea, but the concern people often express is that it could become the basis or justification today for making war against other people. But Israel itself never saw God’s commission to dispose of the Canaanites as a precedent for its relationships with other people. Nor does the book of Joshua imply that Joshua’s action was a pattern for Israel’s future practice. Occupying Canaan and being the means of bringing God’s judgment on the Canaanites was a one-time event from the beginning of its story.

Joshua, Judges & Ruth for Everyone, 3-4.

In other words, object to these Old Testament passages if you must.  But please don’t imagine that you’ll get much support from Christ and the apostles.