In material science, a “plastic” is simply something made of repeated molecules that can be heated to form a new shape and then cooled to retain that shape.
This comes as a surprise to a lot of folks, but there’s nothing in the basic definition of “plastic” that’s concerning in any way. It includes no mention of specific (potentially toxic) ingredients or how long it lasts. A “plastic” is just a type of material with a really useful shape-changing feature.
But when most people say the word “plastic”, they mean traditional plastic, which is the common type of plastic used essentially everywhere. And traditional plastic does have some concerning features.