As human beings, we are hard wired to be constantly on the lookout for potential dangers. This is to be expected. Thousands of years ago, our ancestors had to be ever-vigilant to the threat of natural predators, contagious disease and inclement weather, or suffer the consequences. Today we have largely overcome many of the natural dangers which plagued our forebears, but the same instincts compel us to guard against threats both real and imagined, and heed the call of those who raise the alarm of potential new threats.
This concept has been well understood for thousands of years by those who have sought to control populations.