Ivan, at From Wine to Water, sets out a commonly-used religious argument. In religious conflicts, it goes, religion is the excuse, not the cause. The elimination of religion would not reduce the amount of conflict in the world; we'd simply switch to a different excuse and keep on murdering. It is true that religion doesn't seem to occupy the same fundamental psychological status as things like tribalism and fear of the unknown - but if we atheists accept that religion's not responsible for religious conflict, we lose a key plank of the argument that religion is harmful.
Probably the most common response to this is that hoary old Steven Weinberg quote: it takes religion for good people to do bad things. However, I'd agree with Verbose Stoic that any ends-justify-the-means ethics (especially utilitarianism) can also serve as a motivator for good people to do bad things, countering Weinberg's response as stated. So at the moment Ivan's argument seems pretty solid.
Still, I disagree with Ivan. Why is that? Well, imagine this parallel argument. In war, armies are the method, not the cause. The elimination of armies wouldn't reduce the amount of wars in the world, we'd simply switch to a different method and keep on warring. This is pretty unconvincing, since it doesn't matter whether armies make war more likely - they're a tool of war and should be opposed by people who oppose war.
Religion doesn't create strife (at least, not most of the time) any more that it creates sexism or class war. Instead, religion was created (probably unconsciously) by the same forces that created conflict and oppression, as a tool for justifying and perpetuating conflict and oppression. Opposing religion opposes strife in the same way that opposing automatic weapons for cops opposes police brutality.