Ya, really. There are certain parts of the Bible which are clearly meant to be taken literally and others not. The accounts of Joshua are mostly history, not allegory or spiritual lessons. The Israelis did not make violence a part of their religion, they carried it out whenever they were specifically instructed to do so. Also, the tales of Joshua were war, not "wanton murder" or genocide as you put it. The Bible discourages violence, but it also makes it clear that sometimes violence is necessary. God is not an advocate of genocide or wanton murder, as you seem to make it out to be. I guess my main point is that the Bible makes it clear that violence is normally to be avoided, and if it's not necessary or if God doesn't tell you to, don't do it. That's why the verses you used from Joshua are weak examples at best.
Actually, it is. If it's not didactic, it's not meant to apply. If it's meant for a specific time and a specific place, it does not apply. Plain and simple.
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These arguments are actually MORE VALID for Islam than Christianity, actually.
Islam is a religion based on key religious leaders interpreting the holy scripture; it is a religion that depends on the holy scholars, rather than literal interpretation. That is why there are, amongst the denominations, there are differences of opinion (and splinter groups who make up the tiny minority that become extremists, like the Salafis), and Muslims (both Shi'a and Sunni) are the more spiritual Sufi, for example.
(My emphasis)
A good wiki link with some interesting scholarly thought on the matter.