How do you know that the cast iron seasoning does not leach into your food?
Have you ever had the experience, when cooking in stainless steel, of the oils browning onto the edges of the pan?  You know, the brown gunk that is really tough to clean off...it usually takes a scrub pad, some elbow grease and some abrasive cleaner.  That is polymerized oil.  The idea behind seasoning a cast iron pan is to create a surface of polymerized oil. It's not burnt oils. It is really a pretty tough surface when done correctly.  On top of that you would typically add some fat (for example when searing), though that might not be necessary depending on your cooking method.  The idea that the seasoning would somehow contaminate your food is hard to imagine.  A well seasoned cast iron pan will generally hold up to deglazing...and even a light washing with soap and water.  This is how I think about it as an informed cook.  I would welcome a more informed response from any one with expertise in the actual science.