The Right to Bear Arms
One of the defining Rights of the Petroleum Era, it was common for all sorts of weapons, up to an including heavy military hardware ended up in the hands of civilians, civilian militias and all sorts of paramilitary organizations, terrorists, and separatists. This massive degree of armament made asymmetrical warfare easy to wage against government and professional fighting forces through the Resource Wars and the Second Dark Age. As the old world faded into tattered signs and stories, so did the overriding zealotry of Inalienable and God-Given Rights. There was little point arguing over Rights of assembly or protection from unreasonable search and seizure when there is starvation, disease, or rampant banditry.
Advances in Weapons Technology
The Cosmic Era was born in a bright flash of new technology. Firearms were not left behind in this upwelling of tech. Magnetic weapons became common, ranging from magnetic coil rifles, and linear rail cannons. Lasers, masers, and high energy particle weapons made the move from large scale down to infantry sized weapons. Very quickly, a man in a power armor suit could carry a few weapons and be as effective in combat as a tank of the previous era, or an entire platoon of soldiers.
It was quickly and quietly decided by most sane, self interested politicians that such weaponry had to remain in the hands of the government and government approved organizations. This was the principal impetus behind the Advanced Weapons Technology Non-Proliferation Bill in the Atlantic Federation.
AWTNP (Article 7134)
AWTNP was signed into effect and it created a two tiered system of weapon manufacturing. Civilian grade weapons were given a set of strong limitations to prevent these weapons from being used in rebellions or uprisings. These weapons had limited kinetic potential, muzzle velocity, bore diameter, and specialized ammunition. The only rounds available for civilian ballistic weapons were either soft metallic or frangible composite rounds, both of which are noted for their inability to penetrate even basic SLAB armor, and encounter suits offer good protection against such soft rounds.
Ballistic/conventional firearms using explosive powder propellants are limited to a certain muzzle velocity, and weight of projectile. The resulting pistols and rifles that are created are effective against unarmored targets, such as home invading criminals, protection from wildlife attacks, or rare hunting purposes. Rounds are required to be frangible metallic/plastic composite, plastic, soft metal alloy, or similar materials. These rounds will shatter or disintegrate against standard issue ballistic or SLAB armors.
Magnetic firearms are limited to maximum power capacity of the barrel capacitors, magnet size, and final muzzle velocity. Very few magnetic weapons fall into the civilian grade arsenal, though there are some hunting rifles, and heavy private issue pistols. These weapons require registration as civilian and magnetic weapons.
Lasers are limited to a non-lethal energy output, effectively becoming pain causing, or deterrent weapons and not lethal, unless used in a vicious sadistic matter. Masers, and high energy weapons are completely illegal for civilian ownership.
But What Does it Matter?
The most common weapons available in the Cosmic Era are civilian grade pistols. These weapons are small and relatively weak. Even these weapons are prohibited in locations like Arcologies, seacologies and other enclosed spaces with high population densities. The average civilian isn't armed. Those who are, are only lightly armed at best. When there are civilian uprisings, they are usually armed with these weapons. The soldiers who respond, with power armor, or basic ballistic body armor are very safe from these grade of weapons.
The Black Market is a major source for guns. With the extensive restrictions on firearms, selling military guns can make gun runners ridiculous amounts of money.
Serious criminals and criminal organizations will generally have access to black market guns, making dealing with their organizations much more dangerous. In the favelas and geocities, these heavily armed camps and ghettos are much more likely to be contained or quarantined rather than sending the troops into CQC on hostile ground.
One of the truths behind modern firearm ownership has little to do with self protection, hunting, or patriotism. The thing that no one brings up is that through media presentation, and general opinion, firearms are cool, and badass. Having things that are cool and badass is in and of itself, cool and badass. This Cosmic Era option allows for the civilian population to have access to weapons that are at most a minor threat to national and military assets.