1) There's a long list of materials that are no problem outside your body but that are really bad for you when small pieces get inside your lungs.

2) There's a higher potential harm from new processes and materials that are used everywhere by consumers, versus being used by specialists in exposure-controlled environments.

Because of (1) and (2), if there's anything wrong with this material, the harm will be multiplied.

For example a possibly toxic material used in low-rate specialty manufacturing by protected workers is different from a possibly toxic material that's distributed in fun inhalers inside of cereal boxes.

These concerns are not at all irrational, and are in fact more empirical than reflexive anti-questioning snarkery.

They'd be right to, there are significant health risks to regular glass. People cut arteries while accidentally sticking their hands through panes of it all the time.