How is blinding someone with a laser worse than killing or maiming them with a bullet?
The assorted 'laws of war' are heavily leavened by what their framers suspect that they can actually get at least some people to agree to; but the overall theoretical foundation always seems to be an attempt to steer weapons in the direction of "Kills outright, or leaves a wound that, if treated, will heal with comparatively limited permanent damage."
It's not an easy standard to maintain(both in terms of convenience, mass-maiming is a hell of a shock to morale and logistics, and engineering, something that will kill if it hits you as designed will likely cause serious tissue damage and/or amputation if it scores a sub-par hit); but it's not really a terribly strange shared desire, from the perspective of the warring European powers of the 20th century that wrote most of them.
The one day you'd sell your soul for something, souls are a glut.