Why should the usage of plastics be discouraged?

Plastics can be discouraged because;

1. They are often made from a finite resource such as oil.
2. Manufacturing requires energy & processes can be toxic.
3. With so many types, it can be difficult to identify, sort, collect & process in meaningful economic quantities for recycling. So often end up for ever, never breaking down in landfill sites.
4.Some are incapable due to be recycled, such as thermoplastics due to forming permanent chemical bonds as part of there manufacturing curing process. (These are used in composites such as fibre glass & carbon fibre).
5. The low cost of the items can install a feeling of low worth so can be thrown away after one use despite still being servicable.

It has to be said that plastics have when used properly out perform their equivalents in the total energy balance. This has to be considered before saying plastics are to be discouraged.

Glass vs plastic bottle, The plastic needs less energy to make, is lighter so needs less energy to transport, its tougher, easily recyclable into other things, were as the bottle was collected returned to the factory has to be washed, or smashed before made into more bottles.

Composites of course have superior strength/weight and can be moulded into complex shapes without machining, compared to metals & in aircraft both saves fuel in weight saving & can be formed into efficient aerodynamic shapes (25% less in the Dreamliner I believe).

I have Googled "plastics green issues" and the first up on my search was"Plastics and the environment-the zero waste alliance" pdf which will give further information.

Hope this helps you.