and a social/cultural threat rather than a military threat. I agree with you that the long-term costs and benefits regarding the Middle East are unlikely to be quantifiable, but the US (and everyone else) will still need to be involved there as long at the world still runs on oil. Even a post-petroleum US will probably be continually intervening in the Mideast in some form, because of the great support for Israel among American Christians.
The greatest danger to the United States comes from within, not from without.