In a recent paper the director of the Begin-Sadat Center for Strategic Studies argues that we should not destroy Islamic State (ISIS). It seems a weak but continuing ISIS will make a good magnet for would be terrorists and keep Syria, Iran, and other states weak.
Here we see why Middle East peace won't happen. The author of this paper looks more at keeping Israel's traditional enemies weak (by having ISIS continue to destabilize the region) than at building any sort of lasting stability in the region.
50 years ago in the 1960s the PLO engaged in a political revolt. It had Muslim and Christian groups within its umbrella. While anti-Jewish and anti-Israel, it was largely a secular organization. Today instead of a group wanting to destroy the State of Israel, the Middle East has moved to the point where groups wanting to destroy all non-Muslims (and many insufficiently pure Muslims) are gaining political power and followers around the world.
Do we really want ISIS, with its proven propaganda abilities, to remain even in a weakened state? Will keeping Syria and Iraq perpetually unstable really improve Western security?