Summary: What if truly devastating power was democratized?
The first impact struck New Jersey, but the missed the more populated states. The culprit was a terrorist trying to annihilate the industrial hub of the state, across from New York City. Due to the terrorist's miscalculation, the blast was not as devastating as it could have been. The technology used was potentially far more powerful.
The Photinos were self-contained optical sail spacecraft, originally designed for developing countries. They were small craft with highly-efficient radioisotope electrothermal generators that powered them for decades. Using a system of onboard optical filters, mirrors, and micro-lasers, they were able to achieve relativistic speeds in a few years.
The Photinos proliferated in the decades before the attack, thanks to hobbyist and second-hand markets. Anyone with access to an automated space-based fabber in lunar orbit could have one deployed in a week. A virtual fleet of the craft had been deployed to the rim of the Sol System, and even beyond, as automated probes.
In the aftermath, half-irrelevant governments and megacorporations cited obscure regulations to seize control of all spaceborne assets. However, a far more effective organization already took shape. Comprised of volunteers of small governments, individuals, and hobbyists, they set up an observatory and interception fleet of donated craft, relativistic impactors patrolling the Sol system. Should another terrorist attempt a similar attack, they would deploy a sacrificial craft to impact it.
The relativistic impactors could theoretically annihilate Earth. Those most informed and able to stop such attacks conversely wanted that technical knowledge made available, unlike the Earth-bound authoritarian dinosaurs. Like other dangerous devices or disruptive technologies, they believed an educated public was the best defense.
Together, we prevent the fall of that Sword of Damocles.