Marigolds are members of the chrysanthemum family. Marigold flowers and other flowers of the mums family have been used as a pesticide for at least 400 years.
The ingredient in marigolds that suppresses, kill, and repell lice and mites and darkens egg yokes is Permethrin, the same ingredient found in flea and tick spray. It is also used to kill cockroaches, ants and flies. In a higher concentration Permethrin is found in creams used on adults and children to kill scabies mites and head or body lice.
Bad stuff that Permethrin!
If a commercial cage egg producer sprayed his chickens or their premises with Permeation those eggs or meat birds can not be sold for up to 8 weeks.
But if you call Permethrin a health food then I suppose that you can feed it to your chickens in unlimited quantities as an egg yoke color enhancer, and you can then sell those eggs as "organic" pesticide free eggs like nothing has changed, except that Permethrin color enhanced eggs contrast better with the egg buying publics' green breakfast ham.
Some of us desperately need to think (not rethink) our opposition to things like modern agriculture or commercial egg production because it is clear that we haven't though it all the way through the first time.