We as a species are very horrific.
I think bad things kind of fall into 3 groups:
1. Stuff nature does to you
2. Stuff other people do to you
3. Stuff that happens to you
Stuff nature does to you is like an earthquake. Stuff other people do to you is like a drive-by shooting. Stuff that happens to you is like a terminal illness.
Statistically, about a million people die every week - week in, week, out. That's a solid 50 million people a year who depart this realm. The WHO has a Top 10 list of what causes deaths worldwide:
http://www.who.int/mediacentre/factsheets/fs310/en/
Over a million people die from diarrhea every year...let that sink in, especially in comparison to about 18k murders in the U.S. per year. And in contrast, and not knocking their service & sacrifice in any way, a quick google search says that 4,486 U.S. soldiers died in Iraq and 2,345 U.S. soldiers died in Afghanistan...and that's since 2003 (a 15-year period). If you want to read some crazy stuff, read up on how the 1918 Spanish Influenza Epidemic decimated entire Alaskan villages...be warned that what happened to the babies & children is pretty haunting:
http://www.alaskaweb.org/disease/1918flu.htm
Worldwide, that particular strain of flu killed an estimated 20 to 50 million over a 2-year period. Hopping back over to the war discussion, very few people want to kill other people. In the early days of WWI, they would setup cameras at the trenches to record footage to up their game...and they found people on both sides were shooting in the air instead of at each other, because killing other people was such an adverse activity that people really didn't want to do it. They had to change circular targets to human-being-shaped targets to help people get over that mental roadblock. But ask people on either side & the majority of them would rather go back to their familes & go back to making a living than watch people die & kill people in the field of battle. So even the bad stuff that we do to each other isn't always necessarily choices we make on our own, which is an important thing to note because while there are some people out there who have murder in their heart, most people don't.
Which isn't to say that we aren't all subject to losing control in the heat of the moment...tons of people have been killed in road rage incidents, where they have no prior history of harming other people. The reasons behind inflicting death & injury on other people makes for a long & complicated list, and for the most part, outside of major wars, pale in comparison to the loss of life that nature can inflict:
https://en.wikipedia.org/wiki/List_of_natural_disasters_by_death_toll
The bottom line is that earth can be a scary place, man. We all have both good & bad inside of us. Life is complicated. But things are improving all the time...just look at the last election. Literally almost 50% of the people didn't want the current president in office, and yet there wasn't a huge, bloody riot in the wake of it, which is HIGHLY unusual for pretty much any country experiencing a change in power management. There will always be people doing rotten things out there, and there will always be situations, like getting drafted into war, that force you to make awful decisions. And it's easy to focus on that stuff, if you watch the news all day. Happens to most people I know who retire..they go from being productive & working to sitting around watching a newsfeed of all of the horrible stuff that goes and and suddenly "the world's going to the dogs". Well, the world has always been going to the dogs, that's nothing new! lol.
You can't change the world, you can't change other people, but you can change yourself, and you can affect those around you in a positive way. You can contribute, you can be nice to people, you can help out, you can make a difference with the people you interact with. You don't have to be a troll online or be a jerk IRL - you can make life better for yourself & for those around you, or you can focus on all of the negativity in the world (which again, is quite easy to do). It ultimately boils down to individual choice. I really liked the ending from "Bedazzled" with Brendan Fraser, where they point out exactly that. There's a saying that goes something like, "your perception determines your reality", i.e. what you choose to focus on & what you decide to adopt as for an attitude & outlook on life more or less determines the actions you take & how you feel about things, so if you want to see how bad thing are, the rabbit hole is literally endless...but if you want to focus on just how good things can be, the opportunity for making it so is equally endless.