I think context is important when thinking about this. If another European country was allowing terrorists to reside in their borders and launch attacks on your country AND also allowed another European country to use it's Embassy for planning arms exchanges with the terrorists.
The purpose of the attack was not just to attack some other country's consulate because they wanted to take it out or hurt the workers or civilians. They had intel (that clearly was correct based on who died) that meetings were taking place with terrorists about moving weapons from Iran to Syria for terrorists to use against Israel, the US assets in the area, AND commercial ships.
@Vern who I trust to understand these things better than I do or any article written would, due to her job and experiences in Embassies around the world, has already posted that these types of meetings are NOT to be happening in an Embassy or Consulate. WHY would Iran be holding meetings with Hezbollah in their embassy in Syria?? Why is nobody asking that question? Maybe they were counting on nobody noticing those meetings and looking the other way. I think they saw the chance to take out high level terrorists and leaders of a military that were supporting it and arming them. I would hope that if your country knew the same was going on in a nearby country where terrorists were meeting with military leaders in an Embassy or consulate discussing getting more weapons to be used against your country, then they would act in order to keep your country safe too.