Plastics are a waste product of converting oil to useful fuels. That's why they're so cheap and used in the most unbelievably wasteful ways. They'll remain inextricably linked. Fuel is expensive, plastics are incredibly cheap. If we ban the use of fossil fuels but still rely on oil based plastics, plastics will become very expensive and we'll still be creating the fuel. We'll just have a growing supply of worthless energy sitting around and decaying in storage.

I'm not saying it's a bad idea as I'm not an expert by any means, but to keep plastics for essential uses like in medicine will likely require a heavily subsidized plastic industry at least. But hey we already subsidize the fossil fuel industry directly and by externalizing the planet destroying effects of their use...