Wrong measure. What if men had lower concentration of sperm but higher volume of the ejaculate? Soy is known to have benefits on prostate and much of the volume of sperm comes from prostate liquid.

Possibly wrong measure, and not the whole story in any case.

The implicitly suggested volume measure might not be the wrong measure either since fertility depends on quite a few variables, several we don't even know about.

These unknowns are actually a bit concerning on their own since fertility has been falling rapidly, at least in most of the western hemisphere, and the cause is unknown.

Well, Asia does not seem to suffer yet soy is a significant part of their caloric intake.

Citation required? I doubt it is even 5%.

> Nevertheless, Americans as a whole still consume very little soy protein. Based on 2003 data from the UN Food and Agriculture Organization, per-capita soy protein consumption is less than 1 gram (g) per day in most European and North American countries, although certain subpopulations such as vegetarians, Asian immigrants, and infants fed soy-based formula consume more. The Japanese, on the other hand, consume an average 8.7 g of soy protein per day; Koreans, 6.2–9.6 g; Indonesians, 7.4 g; and the Chinese, 3.4 g.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1480510/

At least it's several times bigger than European and USA consumption.

Citation required for what? The fact that they eat more soy?

Demonizing soy is just a fad. Like demonizing meat or dairy.

Most of USA and Europe eats female mammals like cows and chickens, are we going to make claims that female animal estrogen contained in that flesh makes men infertile? Seems like a much more probable cause than phytoestrogen from plants, not that I would be irresposible to make that argument without any evidence, as is the case for soy.

I'm not attacking soy, just the style of argument.