Plastic guns have their uses. They are incredibly weather resistant pretty tough, cheap, lightweight, and easy to manufacture. I own a few and trust them with my life.
However, plastic has no soul. It doesn't have the look or feel of a well oiled black walnut stock or a deep gloss blue.
I'm also not confident that plastic guns have the same longevity of metal and wood. Maybe some of the newer polymers will last hundreds of years, but from my experience with other plastics, they break down over time, whether it be 50, 100, or 400 years. I expect my quality guns to last that long if properly cared for.
As I speak there is a fully functional 400 year old firearm hanging over my father's fireplace made of brass, steel, and wood. Only time will tell if the new polymers have the same longevity.