The real answer to this is “everything”. Take note of how the negative responses here are long-winded and jam-packed full of facts, figures, statistics and vehement argumentation, when all you did was posit a mild question. People who feel so threatened by even the question of gun regulation that they rant forever on the topic are very, very afraid. Of everything and anything. Their fear is existential, free-floating, and visceral.
An animal that feels cornered, even if it is not, will hiss and spit and posture as if life itself were at stake. Even when it is not.