For one thing, before the 20th century, there were plenty of genocides. We tend to forget about them, partly because they weren't as well documented and partly because, until recently, people didn't care. We used euphemisms like 'sackings' and 'sieges' instead of calling them 'genocides. '
One blob of red in the wrong place and the audience isn't looking at the hero, they're looking at a patch of curtain (or something similar) and your whole effect is lost.