The US became a fearful (and hateful) country because of the media, both traditional and tech/social.

Fear, hate, and other base emotions maximize engagement. A negative story that inspires fear or hate will get often thousands of times more clicks than a neutral or positive one. Media tends to be ad supported and run on attention maximizing KPIs, therefore the media pushes fear and hate.

Social media added a layer of personalized algorithm-driven amplification that dialed this way up, which is why politics has become hyper-polarized and dominated by insane narratives. It drives engagement.

Edit: the reason for this is probably an evolutionary bias toward negativity and paranoia. As the saying goes: If your ancestor mistook a bush for a lion, they lived. If your ancestor mistook a lion for a bush, they are not your ancestor. We are all the descendants of paranoids. Negative media pushes that button.