SratFor comments on the subject:

http://www.stratfor.com/weekly/diplo...608fcc7da4867d

Diplomatic Security in Light of Benghazi

It has been more than two weeks since the Sept. 11 attack on the U.S. diplomatic facility in Benghazi, Libya, that resulted in the death of U.S. Ambassador Christopher Stevens and three other Americans, yet the attack remains front-page news. One reason is that it has become unusual for a U.S. ambassador to be killed. After the 1968 assassination of John Mein in Guatemala -- the first ever U.S. ambassador to be assassinated -- several others were killed in the 1970s: Cleo Noel Jr. in Sudan in 1973, Rodger Davies in Cyprus in 1974, Francis Meloy Jr. in Lebanon in 1976 and Adolph Dubs in Afghanistan in 1979. However, following improvements in diplomatic security during the 1980s, no U.S. ambassador has died as a result of a hostile action since Ambassador Arnold Raphel, who was killed in the plane crash used to assassinate Pakistani President Muhammad Zia-ul-Haq in August 1988...
Obviously not the last word on the subject (nothing ever is), but a real-world look at the situation and potentially some fodder for discussion.

It's worth noting that even if the decision had been made to construct a fortress in the desert it would still be under construction, and there would still be a need to have diplomatic boots (well, ok, diplomatic Gucci shoes) on the ground...