Lead is highly toxic. Plastic is not necessarily toxic at all.
>> A plastics fire in Indiana spewed various toxic chemicals into the air, including hydrogen cyanide and benzene, according to test results from the Environmental Protection Agency.
>> Officials said Friday that air monitors detected hydrogen cyanide, benzene, chlorine, carbon monoxide and volatile organic compounds in the ground-level smoke.
https://www.bennettplastics.com/is-it-safe-to-microwave-my-f...
Do we except polystyrene as carcinogenic, if consumed? So don't eat it. Yet we've banned lead paint, because paint chips flake off. So eating paint chips or inhaling paint dust causes lead toxicity. Admittedly we don't think plastic is nearly as toxic, but some scientists argue it's understudied.
https://pubs.acs.org/doi/10.1021/acsomega.2c03453
>> These adverse effects of PS-MPs [polystyrene] on human kidney and liver cells suggest that ingesting microplastics may lead to toxicological problems on cell metabolism and cell–cell interactions. Because exposing human kidney and liver cells to microplastics results in morphological, metabolic, proliferative changes and cellular stress, these results indicate the potential undesirable effects of microplastics on human health.
Lead has been around for a long time, and well studied. The cumulative "we" are just now coming to terms with microplastics. I think the concern is valid for what these microplastics might be doing to our cells.
https://sustainability.yale.edu/explainers/yale-experts-expl...
>> Anastas goes on to explain that our bodies are accustomed to breaking down, processing, and disposing of natural polymers every day, but newer man-made polymers come with many unknowns. “We just don’t know to what degree these human-made polymers are different and affect our bodies differently,” Anastas explains. “Our bodies evolved to process all of these other natural polymers over countless years, but our bodies and the environment have not been given the chance to evolve to process these man-made polymers.”
Because it's often clear, folks often think that plastic is inert like glass. It is far from it.
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.