Our embassies exist for reasons far beyond conducting foreign policy. Most ambassadors have little responsibility in that area anyway. That's why Hillary and Obama communicate with the upper levels of foreign govts.
Our embassies are there for a number of reasons including:
1. Helping US citizens abroad in those countries, whether they are living/working there or just tourists.
2. Helping US businesses sell products to the foreign country.
3. Accept and process tourist visa for the local populations.
However, I agree with you to an extent. While there are a number of good reasons for embassies abroad (although I question the one in Benghazi, what frickin American citizens are there?) if you can't keep your people safe they shouldn't be there.
Fern
This was a diplomatic mission, in spite of the fact that it housed a full US ambassador. I think it was there because that's where the rebels (or perhaps the least anti-American of the rebel factions) was located and we were trying to curry favor as well as strengthen the most pro-American (or at least, the least anti-American) of the rebel factions. That's a reasonable goal that benefits us all, even if poorly implemented.
I agree that sticking these people there with no security, when other nations had pulled out because of the degenerating security situation and in the face of specific credible threats, was a horrible decision, I just don't think it is a scandal. I think it was a honest decision by State and/or Obama to take a risk in order to curry favor and present the image that Libya was safe under the rebels. If I thought this was for domestic politics I would be outraged, but I don't think anyone in America would be swayed against Obama if our diplomatic mission was protected by a Marine squad or a SF heavy team. Only Libyan politics would be affected. I imagine that State was hoping that if/when our embassy was attacked it would be Libyans than Americans killing Libyans. Of course, all of us know that when the radical Muslims attack the less radical Muslims simply get out of their way, but hope springs eternal in the pin-striped breast.
The cover-up was for domestic politics, but probably more so for good old-fashioned interdepartmental turf war ass covering. I'd still consider it a scandal had they made up something from whole cloth, but it seems to me that Obama simply picked the most politically appealing narrative from those possible, even knowing it wasn't true, to blunt the political impact. To me that's meh; politicians are always going to look for the most politically useful explanation, not the most truthful explanation. I voted for Romney (and have before), but I don't think his behavior after the incident was materially different.