There are rules, conventions, against such things. Forget killing. Today it is very possible to build a laser capable of blinding a person at range. That wins any dogfight instantly. The first concepts of the f22 were to have an lcd cockpit to counter such threats. But nobody wants to fight a war where mass blinding is a thing. As with plastic shrapnel, some things are just too horrific. Nobody builds them and so even those without rules never get a chance to use them. There is no plastic shrapnel in even the most vicious of IEDs.

(Plastic doesnt show on x-rays.)