They leave them lying around their houses, on their coffee tables or in their bedrooms, where small children often happen upon them, often with predictably tragic results. Thousands of children are killed annually by these weapons. Lawsuits against the manufacturers might recover some of the costs to the community, but that will provide little comfort to those who have lost loved ones. It is beyond dispute that the most devastating firearm short of the atomic bomb is fire. As technology is used to refine firearms, there is a tradeoff of lethality for precision.
Complexity is added to achieve precision and control at the expense of destructive power.
More deadly firearms require less technology, and are easier to make. Bombs are easier to make than guns, and fire is more easily made than bombs. Complex firearms generally kill or injure one person per shot that hits. Less complex firearms, such as more easily made bombs, destroy the intended victim, plus anyone nearby, and sometimes the building they are in. The least complex and most easily produced firearm, fire, often doesn't stop immediately as a bomb does, but continues on, destroying for quite some time.