Not to split hairs, but the bacteria qualifies as an impurity by any definition. You also left out the most important reason for pasteurizing raw honey. Raw honey can and will ferment on it's own due to the amounts of wild yeast cells that are prevalent in hives and thus are present in the honey. Not to be overly technical, but since the mead's I make can take a minimum of 4-6 months before they are ready to bottle/keg, that's plenty of time for the wild yeasts to impact the flavor.

Honey is to dry for spontaneous fermentation via wild yeast. This is basic chem/bio having to do with osmosis and diffusion. This is why mead benefits from mild degassing before the 1/2 sugar point - makes the chemical migration through the yeast cell wall more favorable. Every comment I found about 'spontaneous fermentation of wild honey' also mentioned the addition of water first (sounds like mead/beer/wine making)
If there is fermentation in the hives, I'm not surprised, when the bee's bring in the nectar, it is close to 2% sugar and 98% water. The bees then dry the nectar and make honey. When honey is ready it is close to 70% sugar and 30% water. Big difference.
The splitting of hairs began in my other post. The problem with saying "impurities" is that bacteria are not the only ones, there could be to a lesser degree heavy metals - which would be another reason to not let infants near the honey, but unless China *1 is getting into our markets, is a reason to fear infants eating honey. Specifically it is the bacteria that is the warning for honey.
As to wild yeast contaminating mead, or other products. I came across one article that had sampled homebrews and found there were bacteria at varying levels, and the less the better in the beers.
Another article I came across found that for Meads, those where the honey was heated prior to fermentation tasted worse. (can't find the articles now). Thus those wild yeasts were in the better tasting meads. Probably because heating honey drives of some of the more volatile flavors.
Typically we put in our own yeast at something x10K or more the amount of cells as a wild yeast or other bacteria would have giving it a massive head start. I think a working definition of sanitation is 99% of the bacteria dead, leaving something on the order of 10K, we put about 100M(illion) yeast in. *2
*1. Lead or other toxic impurities in China's honey is a different thread entirely. The bullet sum up is buy local honey from trustable sources.
*2 Sanitation is not "measurable." This compares to "sterilization" which I think is 99.999% bacteria free, and can be measured, documented and failures lead to prosecution. Think of the difference between these two as "salt to taste" and "add exactly 1/4 teaspoon." One is not very defined (sanitize) but generally understood. The other is very specific(sterilize) and measurable and in some ways less generally understood.