Is LEGO element damaged at the molecular level when rubbed with rubbing alcohol?
The LEGO Group has been extremely careful about the formulation of all of the plastic parts they manufacture.
I do not believe they ever used lead in any of their parts. Decades ago they removed cadmium from the yellow pigments.
I have never found that isopropyl alcohol will soften the plastic used for Lego bricks.
What will soften Lego bricks is hot water. Do not use a dishwasher to clean Lego bricks. The water is too hot and the detergent is too aggressive.
To clean most Lego brick mild soap and warm water is the best choice. Air dry only, do not use hot air from hair dryers.