I aggree that it's a bad idea to start discussions about morally questionable political decisions, including wars, genocides and so on. That likely won't lead to anything good.
But in some way, nature has some examples which should be less dangerous to discuss.
Just think about the process of eating. Every organism must do it in one way or the other, in order to gain energy and keep its metabolism working. If you stop eating, you will die. But many organisms do this by preying on other organisms in some way. Herbivores feed on plants, carnivores feed on animals, etc. Sure, there are also scavengers, but our complex ecosystems would not work solely with them. So it needs "evil" creatures who harm and kill other creatures for food. Many of those "evil" creatures are themselves prey to some other predator, what can be said to be the potential "price" they pay, as their predator keeps itself alive by the same "evil" strategy. (Then there is also parasitism which has a similar function, but let's not get too much off-topic.)
Us humans are biologically omnivores, so we keep ourselves alive basically by eating both plants and animals. Some of us may become vegetarians and thus no longer "prey" on animals, but we can't completely avoid eating things that lived once. No matter what you do, if you want to stay alive as long as possible, you will necessarily benefit from harm being done to some kind of creature.
Is this understandable?