It's a good question OP, and there's no straightforward answer.
You should know that it isn't crazy or irrational to be horrified by the atrocities people are capable of committing. It's a very real horror. At any given time, the amount of suffering being experienced is unfathomable. Children starving to death, people skinning animals alive, people torturing each other, people losing loved ones in all sort of horrible circumstances...
There seem to be four main ways of dealing with it:
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Think about it on repeat, carry it with you everywhere you go, so that when you're talking to people you think, "You'd kill me if you were a concentration camp officer and I was a detainee, the only thing stopping you is circumstance".
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Don't think about it. Block it out. Bombard yourself with positive things that you like, calming music, green tea, yoga. Write down things you're thankful for every day.
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Get riled up about the injustice and become an activist.
I can't tell you which one is right for you. I personally don't recommend 1 - I did that for a long while and became very, very down. 2 is fine in moderation, but if you switch off to everything you'll end up disengaged. This is sort of fine if you're a good person and live a good life, but if you genuinely don't know what's going on in the world you'll become a bit stupid and open to manipulation. I find full-on 'number 2' people rather toxically positive at times. 3 is good for the planet, but you need to be a certain type of person. I'm not and I feel guilty that I'm not.
I sometimes wonder if the answer is a mix of the three. Do allow yourself to process the horrors of the world, but after a little bit (set your own time limit) stop, and then move onto something else, such as something you like to do or need to do.
I suspect that as with most things, it's all about balance. Yes, humans can be absolutely horrific, and unfortunately, I can't see that changing given our biological make-up. Society might change, but the susceptibility won't. On the flip side, humans can be really great, too - incredibly caring and selfless. It's worth seeking out examples of this to remind yourself.