Any hole introduced to a structure - whether drilled, bored, reamed, burned or melted is a point of weakness and a stress raiser unfortunatley.
Some locations make that effect much worse, such as at the end of beam/cantileaver that is subject to movement at the extremities from the pivot/mounting point, especialy high speed oscillation (vibration) like at the end of the mudguard/fender.
Melting would seem better than drilling (and reaming for better surface finish to reduce risk of cracking), but the brittleness and hardening of the plastic from the heat would more than likely make the situation worse and speed up the cracking process - engineering is always a compromise.
Some locations make that effect much worse, such as at the end of beam/cantileaver that is subject to movement at the extremities from the pivot/mounting point, especialy high speed oscillation (vibration) like at the end of the mudguard/fender.
Melting would seem better than drilling (and reaming for better surface finish to reduce risk of cracking), but the brittleness and hardening of the plastic from the heat would more than likely make the situation worse and speed up the cracking process - engineering is always a compromise.