Well, we expect scientists to be conservative and skeptical but science aficionados are not so kind with public conservatism when they say "Hey--do this! It's perfectly OK. NO side effects."
It takes a while for reports of side effects or toxicity or whatever from new products. But Teflon is not new.
Some minimal or long-term effects are hard to trace, such as radiation, because of complex environments--as you mentioned, hamburger. Let alone the profit motive--it took forever to declare smoking dangerous!
Researchers are unlikely to spend the bucks to establish whether Teflon fumes or x-rays plus TV plus sun plus microwave ovens plus living downwind from a nuclear reactor, or eating high-nitrite foods cooked at too-high temperatures, plus- plus- plus-_contributed_ to someone's cancer or eventual untimely death.
I think there is reason not to worry much about Teflon, but even its defense is eroded by bad logic and inattention to, "What if you DO accidentally leave the pan on high burner undetected and your bird dies?"
It is possible to analyze complexity, but abundant and careful observation, experimentation, and rigorous thinking are critically important to such undertakings.
Or so it seems to me. I think it's hard to think logically in a world rife with advertisements and bullying. I wrote the administrator/s to see if we could have a standing logic thread under "resources", but I haven't heard back. I could use the practice myself, so I'm not just trying to give our friend a hard time. We need the practice and so do students or questioners who ask the experts.