Gun control.

Some governments will try/succeed in limiting your access to firearms and ammunition. There are positives and negatives to this.
The positives are less people will get shot by accident, less nut jobs will have them and rednecks can't stockpile them in their backyard sheds.
The negatives however, criminals will still have the guns, it can lead to uprisings etc.

Now, there are ways around this, some practical and some not.

A good way to defend against random criminals with guns in your house, when you have none, is to find something more frightening than a gun. Get creative. Make a air cannon that fires shrapnel at them, put a punji stake pit right inside the doorway, put a fake claymore mine in the entrance to your room etc. Basically, bring an unnecessary level of violence to the situation. The weak willed will back down when you show that not only do you have a back bone, but that you are also capable of ripping theirs out and using it as a coat rack.

They bring a knife, bring a chainsaw.
They bring a pistol, bring a grenade.
They bring a shotgun, bring a cannon that fires an explosive chainsaw.
They bring a machine gun, bring 20 pounds of C4.

If they want to bring violence, take it to the next level. Make it excessive to the point where they won't think it's worth it.