I still don’t fully understand. Would there be unwanted gasses coming out? Could we not burn the specific plastics where it’s economically worth it for electric

I still don’t fully understand. Would there be unwanted gasses coming out? Could we not burn the specific plastics where it’s economically worth it for electric generation? I don’t know the full science so my assumptions might be wrong but I wonder how much worse it is compared to coal and natty gas plants?