Personally I am terrified of plastic. Plastic bottles, for example, scare the hell out of me in terms of their long-term impact on the environment - think about the petrol spent for transportation, the factories making them, the empty bottles ending up in oceans (and eventually in the frightening "Pacific trash vortex" - Google it!)....
Moreover, a combination of plastic and extreme temperatures has been linked to potentially causing numerous cancers since acute heat/cold help release chemicals from the plastic (after all, it's made from petrol) - whether the plastic bottle is left in the car on a sunny day, forgotten in a freezer overnight, or boxes of them are stored in a delivery truck that will most likely spend days on the road.
A lot of people heat their lunch or even meals in the microwave ("nuke it!" as they say in Oz) in plastic containers - plastic which is usually of very cheap and poor quality. Whatsmore, research reveals that microwaves pose a very high health risk. Again, you should research it if you remain doubtful.
I personally try not to use the microwave (of course it's not always possible), preferring instead to reheat my food in the over or in a conventional pan. And that's when Aussies look at me with their eyes wide open - "but that consumes way more energy!" they say. "It's obvious you're not the one paying the electricity bill..."
As it turns out, it is very common here to nuke your food. But to ensure that it doesn't splatter, you must cover the container with cling wrap (a.k.a. Saran Wrap). People do this at home and at work. Why waste electricity boiling water to make steamed vegetables when you can nuke them in 2 minutes and save precious energy?
My answer is: health - the same reason that I despise using plastic kettles. Plastic isn't bad in itself, but research reveals that the use we make out of it greatly increases health risks.
To quote Dr. Edward Fujimoto "the combination fat, high heat and plastics releases dioxins into the food and ultimately into the cells of the body. Dioxins are carcinogens and highly toxic to the cells of our bodies."
Instead, he recommends using glass, Corning Ware, or ceramic containers for heating food. You get the same results, without the dioxins.
According to the U.S. Food and Drug Administration, chemical components can indeed "migrate" from plastics into food at microwaving temperatures.
Plastic is made of various components including DEHA and PVC.
The State of California is currently considering a bill that would ban the use of PVC in consumer packaging due to the threats it poses to human and environmental health and its effect on the recycling stream.
More (interesting) details can be found on Wikipedia (from different sources) :
Plasticizers that must be added to make PVC flexible have been additives of particular concern.
Because soft PVC toys have been made for babies for years, there are concerns that these additives leach out of soft toys into the mouths of the children chewing on them. Phthalates mimic human hormones and also affect various life forms including fish and invertebrates adversely. Additionally, adult sex toys have been demonstrated to contain high concentrations of the additives.
Other vinyl products including car interiors, shower curtains, and flooring initially release chemical gases into the air. Some studies indicate that this outgassing of additives may contribute to health complications, and have resulted in a call for banning the use of DEHP on shower curtains, among other uses. The Japanese car companies Toyota, Nissan, and Honda have eliminated PVC in their car interiors starting in 2007.
Plastic is convenient and pretty much everywhere you look - thus I find it hard to avoid. But I like to choose other materials over it, such as metal bottles or eating out of a tuna can. However traces of plastic coating have been found even in metal containers. As we say in French, "on n'est pas sortis du bois...!!"
