Fermented foods, which are largely considered good for heath, are full of yeast.
So you could refine that last bit to
> We're taxing and confusing our immune systems by eating.
if that were truly the case.
Well this is not wrong. I'm no expert, but it seems as though not eating (or drinking) would result in less need for inmune system activity, at least in the digestive track. Of course, you'd die, but maybe that was the cost of healthy living all along
I can easily imagine someone with a genetic trait that malforms a single protein could end up with a heritable sensitivity to one particular yeast strain, and not all yeast, everywhere.
Fermented foods and mushrooms can be good at fighting cancer precisely because they ramp up the immune system. In fact yeast is used as an adjuvant inside of vaccines for this purpose.
What's insane is that it is both known and not known that yeast causes inflammation by science. Used as adjuvant, used to "boost" immunity, yet not understood to be a cause of general low-grade systemic inflammation when in our food supply.
Opportunistic Strains of Saccharomyces cerevisiae: A Potential Risk Sold in Food Products https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4705302/
Though I guess it will have as much wild yeast land on it as any other food in your plate but I don't think that's what the parent comment was referencing.
Source: I've been involved in small commercial cheese making for years.
For example, Dectin-1 is one of many innate cellular receptors that launch inflammatory responses when Bread yeast (and others) is detected (and possibly 1,3 beta glucans from wheat). We are in a genetic war with saccharomyces cerevisia, inside of our DNA. And not just us, all animals need to be in this war, because otherwise we'd die.
https://en.wikipedia.org/wiki/CLEC7A
So if all this is true, does it make sense to put yeast extract in your gravy tonight?