The official view is that there’s no health risk involved; it’s simply a matter of misrepresentation. If you label a product ‘beef’ it’s supposed to be made of cow, not horse. That’s fair enough, but I’m sure there are also two other factors involved.
The first is the matter of cultural sensibility. We British regard the eating of beef as being ethical because the cow is essentially a farm animal, whereas the eating of horse meat is deemed unethical because the horse is a pet animal. The logic behind that argument is surely questionable.
The second is the sense that the horse meat amounts to an unclean contaminant, thereby making the product not only mislabelled, but inferior. Well, it seems to me that if people could see exactly what goes into processed beef products, they might come to the view that containing a little healthy horse meat is of relatively minor concern.
Since I’m a vegetarian, of course, none of this matters a jot to me.