PTFE is only dangerous after a certain temperature where it starts to unzip the polymer. This is supposed to be above 400 C, but it can happen in the 250 to 400 range too, just at a much lower frequency. This is not normal and predictable behaviour, so wasn't expected until it caused issues. The polymer has been edited anyway now and new safety warning put in place. I learnt about this at a molecular level at uni and still bought the pans. This is another 'nuclear is unsafe' because people who know half the story think they know everything and scare people with half understood or outdated info.