Polymers are very useful, but they cause problems. Most are made from chemicals obtained from crude oil. Crude oil is a non-renewable resource, so once it is used up it cannot be replaced, and supplies of starting materials for polymers will run low.
Most polymers are non-biodegradable. Microorganisms cannot break down the long chains of carbon atoms, so waste polymers do not rot. When buried in landfill sites they persist for hundreds of years and take up space. Polymers dropped as litter can also harm wildlife.
Burning waste polymers gets rid of them and can release energy, but it produces carbon dioxide, which adds to global warming. Burning PVC also gives off toxic hydrogen chloride gas. Recycling avoids these problems, but different polymers cannot be melted together and reformed into one good product. The waste must be sorted by type first, which takes time and money.