Frankly it is. Read the relevant international convention. Salala and this incident are two completely different things. I agree that the Americans are not well liked by most of the people worldwide but that still does not change the rules that give diplomats immunity.
Once again, a diplomat is expected to observe the rules of the host country. It is not as if they can go around and do whatever they want. You can always evict them but that is it. It will cause a row in your relations, you can berate them in all international forums and use diplomacy and your relations with other countries to join you in this condemnation and to get some reprieve for the affected family. However, I doubt we will ever go this route and, once the news dies down, it will be business as usual.