Cane, you could cause me to write a book asking questions like that and I don't have time. I need to go cook down some tomatoes. To me part of it is that legally we live in a risk free environment. If something could possibly have any kind of bad effect they have to warn us about it or risk getting sued. That's why a step-ladder I got years ago had the warning that if you step on any of the steps on that ladder you might fall off. Not just the top steps but any of them. Supposedly that would protect them in a lawsuit if someone fell off. That thinking has carried over into lawmaking bodies, they have to be absolutely risk free.
The WHO is not a lawmaking body, it's an organization that is trying to improve the health of people around the world. They are the ones trying to eradicate polio and reduce the huge number of yearly deaths from malaria so they do physical things. A big part of their job is to educate so they offer advisories. Sometimes treaties are written and ratified where we or other countries agree to work with the WHO but the WHO can't dictate to us, we are still a sovereign country. Should you care that they say? Should you care what the surgeon general of the US says?
I agree with Seed. Practically anything has something potentially harmful in it, especially if you are allergic or sensitive to it or if you overindulge in it, dosage is important. The young, elderly, or weak are more susceptible to many things or dosages that wouldn't phase many of us. Since the goal is zero risk they offer a lot of warnings, even if the risk is pretty low for a majority of people.