Not idiotic at all. The host country is responsible for protecting diplomatic missions. We do it in the US. The Bureau of Diplomatic Security is responsible for assisting foreign embassies and consulates in the United States with the security for their missions and personnel.
If we don't have host country assistance to provide security assistance, then there is no way we can defend our embassies. The issue with Libya was that there was no real government in place, especially in a place like Benghazi, to provide that assistance. We should not place our people in such places period.
The purpose of US furnished armed protection for diplomatic facilities abroad is to buy enough time so the host country can come to our assistance.
However, in the case of Lybia is it a country that has the capability of protecting a facility? Does the presence of terrorist-related groups make that abundantly clear?