Probably every person who cooks has cut themselves while preparing food. Blood can carry many pathogens, so continuing to prepare that food may incorporate those pathogens into the food. Unless it is going to be cooked thoroughly (by that I mean at least 160°F/71°C in the center) it seems prudent that the food should be thrown out, even though it seems a waste.
For food that is going to be served raw, while hydrogen peroxide will probably destroy the blood and any pathogens it may carry, it can also destroy the food or alter its taste, and it may not be 100% successful. And getting the correct H2O2 concentration may be guesswork, at best.
So should we toss the food? It certainly seems the prudent thing to do. Better to waste the food than get sick. Let's assume the blood either got incorporated into the food (not splattered on a nearby surface) and/or the blood was noticed so late that it seems likely that the blood got in to the food. If preparing raw food (salad e.g.), then the blood probably got well mixed with the food, thus making its removal nearly impossible.