The cleaning step.

Steps one through three are what is called "seasoning" the pan. It's a process that often makes a bunch of smoke. Ideally, you only ever have to do that once. Cooking on cast iron doesn't produce a smoky mess.

If "seasoning" the pan achieves anything at all, doesn't it necessarily have to result in some sort of coating of the pan's surface?

Yes. Seasoning leaves a baked-on coating of oil/fat. That doesn't mean that the coating is carcinogenic.

IIRC (and I might not RC, I'm no food chemist) the coating is polymerized oil/fat and completely harmless.

At smoking point, carcinogens are created both in the gas and what's left behind.

How sure are you that the non-stick coating left on the pan is more carcinogenic than browned hash browns?

What makes you think the pan's surface is more carcinogenic than the steak crust?

I don't, but I'm not sure that's relevant to the hypothesis that cast iron pans are less toxic than teflon pans.

It's been a while, I'll follow up anyway...

I don't use cast iron pans because I believe they're less toxic, but because they make a damn fine crusty steak or fried potatoes.

And I use teflon pans to stir-fry or steam veggies and chicken, or to make fried eggs, just because they're more convenient.

To be honest, I don't really care all that much about potential toxiticity in cooking equipment. That wasn't really my hypothesis to begin with, I was just sharing my love for cast iron pans :-)