Not the last drone attack to come.
Likely the drone(s) that attacked oil facilities in Saudi Arabia were not some small quad-copter drone. Given the amount of damages and the time to repair, it/they were likely larger and perhaps fixed wing aircraft. The impact on oil prices has been immediate, see Crude prices jump 12% after drone strikes halve Saudi oil output; Trump says U.S. to tap strategic reserves.
I've been expecting that eventually we would be seeing this type of use for drones. The next threshold to be crossed will be attacks on soft targets, like stadiums, that might have metal detectors today, but no drone defenses to keep aircraft from just popping over the stadium wall and detonating a pipe bomb.
The above should not deter people and organizations from using drones to enhance their internal agency's capabilities. Cars are used for many different criminal acts, yet they have a huge benefit to the rest of society and its functioning. I remain concerned that uninformed legislation at the state and local levels could restrict the benefits of this new technology.
Keep a watchful eye on legislative agendas and work to oppose those perhaps well-intentioned, but misguided, efforts to restrict their lawful use by government and industry.