Cast-iron cookware seems to get a lot of paleo love. I have trouble understanding how it could really be healthy. But perhaps my concerns can be dismissed. (I would love to have a healthy non-stick option).
1) The seasoning process seems to involve oxidized, polymerized oils, unsaturated fats and high temps even preferred. Regardless of type of fat used, it seems to very much be a chemical breakdown-free radical sort of process. Exactly what we WOULDN'T want going on while cooking. So are we confident the resulting seasoning layer does not leech harmful bits into our food during normal cooking? Is anything 'bad' gone after the seasoning process or safely 'locked away' in some sense?
2) The typical process of using it seems to involve intentionally leaving oil on the pan in between uses. Won't this go bad, even saturated fats? And even what we think of as predominately saturated fats would probably be some % unsaturated, hence definitely go bad.
3) Similar to #2, wouldn't old food bits tend to be left, perhaps in very small quantities, due to limited cleaning methods. (Perhaps not an issue with thorough cleaning, but that tends to go against protecting the seasoning)
4) I've seen it mentioned that iron itself can act as a catalyst to increase fat oxidation.
5) Have also (once) seen the claim that the form of iron we would get is not the kind our body can use (and potentially harmful). No idea if there is any merit to this.