I don't know that's what they feel they need.
What I have seen stated is not that they need to have always-evil things to have conflict. It is that they want conflict and its resolution to be simple, unambiguous, and stress-relieving. The real world is complex, and nuanced, so they want to be able to just punch people n the face without worrying about it so much in their entertainment game.
Reading this and thinking about what has been said so far in this thread I realized I probably haven't made it clear why this doesn't work for so many of us. So I'm going to ramble a bit here. I hope people who think this way will follow me on this little journey, and hopefully understand why emotions are high.
I personally sometimes do like simple action focused stories myself, and I don't think you need evil for it. Saying evil doesn't exist doesn't mean you have to think about every opponent you come across. Just because the swordsman in the Indiana Jones movie isn't evil by nature doesn't mean you have to wonder about his motivation and discuss his moral standing. Most human beings enjoy violence to some extent, as long as no one actually gets hurt in the real world. This is a natural part of human nature that can be explored responsibly. It can be escapism pure and simple. This naturally begs the question I'm sure some of you are thinking, if you're not thinking of the implications all the time, what is the difference between an opponent being evil or not?
Let's take a simple example of the stereotypical evil orc game. Zoomed in, viewed encounter by encounter it may look no different weather they're evil or not. Then near campaign's end your party gets a mcguffin that allows you to
take care of the orc problem, permanently. You do it... right? By the logic of the campaign, it's the only reasonable conclusion. Orcs are pure evil, they can only hurt everyone in the world and never be redeemed. It
is the right decision, you couldn't even argue otherwise. No matter how correct this line of thinking is in the game world, for the people playing the game this can be a disturbing and dark conclusion. This is the disconnect, having true, pure evil species in a game puts you on a dark path.
I think most people can agree it's fine to kill a fly in the real world, but it's a lot less fine if someone traps and tortures the fly. Plucking it's wings off under a magifying glass to prolong it's suffering. Laughing at it and encouraging people around them to watch it twich. Likewise it's fine to have consequence free violence in a game, less fine if someone is enjoying the pain and suffering they are doing in game, and something being evil is the best excuse for this behavior. I'm sure most DM's have a line with this sort of thing and will not let it go too far, but again, having evil in the game puts you on this dark path. Even if you don't follow it yourself, it is there and it encourages you to walk further down it.
And this has some real world implications as well. You can say you understand that this is fiction and not how the real world works, but play can subtly influence how you think. Particularly if the wider culture encourages this line of thinking. It makes it just a little more natural to think in black and white terms. The more you act out good and evil in play, the easier it is to reflexively, instinctively, think in terms of good and evil in the real world as well. Again, you're on a subtly dark path.
The path is always there, it encourages you to walk it, it leads to only one conclusion, and this disturbs those that think about it.
I cannot know for sure how others think about this. Maybe it's completely true that this path doesn't exist for you. That it exists only in my mind. All I can say is it
does exist in my own mind, and I cannot unsee the implications. I see the path and it disturbs and repulses me in the most profound way you can possibly imagine.
The other posts I've made in this thread were easy for me to write. This one was not. It is affecting me emotionally, and I have stress that I'm not conveying my thoughts properly. I'm shaking just a little. That's how much this topic means to me, how much it affects me. Even if you will never see the path yourself, I hope you understand where those of us who do are coming from. Why it's a deal breaker. We cannot unsee.