Did you know that bubble gum is made from plastic and rubber? It used to be tree resins (which sounds odd enough, but then again, aspirin came from tree bark, and that's worked out well), but in order to save money, it's now made from plastic.
So, if you spend a lot of time making sure your kid is drinking from BPA free water bottles and carries a waste free, metal lunch box, why would you let them chew plastic?
Because you didn't know, of course. But now you do.
Beth Terry mentioned this in her blog, Fake Plastic Fish, but I missed that article. Give it a read. It's eye opening.
Knowledge is power. Be powerful.