From what I gather, asbestos is also very stable and not reactive. Asbestosis is caused by tiny fibers physically tearing your lungs.
It’s unlikely that plastic is as dangerous (we’d seen it by now) but its buildup can likewise cause some condition.
You folks are living in the stone age. In the current millennium, plenty of consumer-grade pre-built planets are available.
All you have to do is occasionally spend your weekend debugging incompatibility of gravity and quantum layers.