People don't typically set plastic on fire to inhale the smoke. But leaving a water bottle in a car, where there are often significant thermal changes, results in a leaching of some of those chemicals into the water.
Because it's often clear, folks often think that plastic is inert like glass. It is far from it.
The (sub)topic is lead, though. If lead is still being used in plastic water bottles, then I'm with you, that's just nuts.
Obviously water bottles should be made from plastics that don't leach anything harmful into the water when left in a hot car. To the extent they do, it should be easy to come up with specific arguments to prohibit specific substances. Just blaming "plastics" in general is a category error, since not all plastics are proven to be harmful in this regard.
