The poster was using the phrase natural dye.

It’s a naturally occurring non organic molecule, but it’s not naturally a white pigment. It takes a lot of processing to get that brilliant white powder and as such it’s not something our ancestors dealt with.

It is not naturally occurring in the human diet.

This is the same argument people use against bread, and against meat.

Huh? Our ancestors have been eating meat for 2 million years. We know because bones do not biodegrade so we've found many prehistoric bones with tool marks left when prehistoric people cut the meat off the bone.

So is arsenic.

Totally off-topic, but your comment reminded me of some lyrics to a song by one of my favorite folk singers [0]:

  [Weed is] jus' a plant
  Like poppies and sugar cane
  Coca and some science make some good cocaine

[0]: https://youtu.be/ixE73z_a37U