Consumer choice; harmful environmental aspects of polyethylene vs polypropylene
Every material is terrible if not properly collected and processed after use.

Wether you re-use it (like glass bottles), or recycle the material, or burn it to make electricity and district heating, is small potatoes. 

What material you use is also not very important, only the actual energy and environmental costs of "bio"materials like paper or cotton are very high. You have to re-use them very often before they make sense!