When people are exposed to the same upsetting thing over and over again, either it fucks with their mental health and makes them more depressed and anxious, or alternatively it makes them apathetic and desensitized. Neither of those things are good for a movement, and those are the ways humans are going to react to constant upsetting messages. You cannot avoid this by telling people to just be better people, you cannot use higher reasoning to make an entire community's emotions work in a fundamentally different way to how human emotions normal work.

Every successful movement account for the fact that people can't be at 100% all the time. Movements that ask for a level of extreme and undying anger, burn bright and die fast, it's a useful way of organizing a very immediate response, but cannot be done for something larger scale. If you give people, the ultimatum of either being at 100% or 0% all the time, they will choose 0% because the alternative isn't possible for most people.

If you're constantly showing the same disturbing images over and over again, they will lose their effectiveness quickly. If I see a post detailing the horrors of the current genocide, I'm probably just going to scroll past it, because it's all things I already know, and I've seen it so many times there's no emotional reaction, and this is how a lot of people are with posts like this, because you can't ask people to have the same emotional reaction to the same information hundreds of times over.

You can't stop activist burnout by being a better person because burnout isn't a choice, it's a psychological response. If your activism doesn't account for the material reality of the community (in this case being humans with human minds), then that's on you for organizing badly.