Historically, we’ve always been pretty awful to each other. A lot of our cutting edge science has revolved around ways to hurt and kill each other since the first human realised it was easier to kill the person pissing him off with a rock than their hands.
In the last 100 years or so however, those weapons have become powerful enough to end us as a species and I think you’d be hard pressed to find a type of weaponry that, once invented, hasn’t been used and I’m not sure we’ve evolved enough empathy to prioritise not killing all of us over not killing the country/group who are currently annoying us.
It’s pretty understandable therefore to have a realistic fear that there’s a very good chance we’ll bring about our own end.