Humans invent lots of stuff. I would say mostly good and useful stuff. After all, we want to improve the quality of our lives, not make it worse. But because of the human nature, which is by default inclined to evil, people take even the best inventions and use them in bad ways.
Recently there was a big debate in the US over gun control. "Guns don't kill people. People kill people." It's true, guns don't kill on their own (no object really does anything on its own), but guns were specifically invented to kill. And no good comes from killing.
Another argument was :"The only thing that stops a bad guy with a gun is a good guy with a gun." The truth is, no mass-shootings in the last 30 years have been stopped by a "good guy with a gun" from the crowd.
So, to say that : "good inventions can be used in bad ways" applies to guns might be a bit inappropriate, because I can't consider guns to be a good invention. (Knives are not the same thing. They are used mostly for daily activities, and killing 50 people with a knife is almost impossible - the police or other people can come and help- while doing the same thing with a gun is relatively easy and others are much less able to stop the situation.)
Now that we got that out of the way, what I was thinking about and what gave me the idea to talk about this topic were nails. Yes, the kind of nails that you hit with a hammer, and use to build, to hold things together and to hang paintings on the walls. They seem like a good invention. They're not hard to produce, they're easy to use and durable. But, as I said before, humans found a way to use them for evil purposes. Nails made for joining two pieces of wood were used to nail human flesh to wood, to hang humans on crosses instead of pictures on the walls, and most heart-breaking of all, to nail the Son of God on the cross.