Let's speak ethically for a bit.
I think that land mines are the worst weapon.
Tactically, they're used to slow down movement and secure borders. It could be said that they're more of a deterrent - simply knowing that there are landmines ahead of you is enough to bring you to a halt. They also serve as a force multiplier - they boost the defense of an area without needing any more people.
Land mines are not designed specifically to kill. Killing is a side effect of the blast. No, land mines are designed to maim. To incapacitate you. To tear your arms and legs from your body. To blind you with your own blood and charred flesh.
This, in itself, is an unethical tactic. Sure, to you an incapacitated enemy is just as good as a dead enemy - neither can fight against you. But what of the victim? Is it a requirement to be humane during a war - to kill, but not cause unnecessary suffering, even to the enemy? The enemy, for the most part, is just another soldier doing his job. Should he be confined to a lifetime of hospital visits, sitting in a wheelchair, burns covering his bandaged face?
Let's not forget that landmines stay in the ground after conflict. Quarrels between two nations can become calm, but does that disarm the land mines? No. These horrific remanants of an old conflict can still cause further pain. As far as they are concerned, the war is still going on, and they lie, waiting for that footstep so that it may do its job. Its job is to maim, and it does so indiscriminately. Soldier, civilian, animal, child. It doesn't care.
It is estimated that over 75 countries are plagued with land mines.
That is why land mines are the worst weapon ever.