It makes sense from an evolutionary perspective, I suppose, because our brains disproportionately weight the importance of adverse risks for survival (#prospecttheory). So, if you have reason to believe a spider is a real risk, your body will act like it for self-preservation.
Somewhat related to your thoughts...
I can't find the original source (sorry!), but I read a news article last week that touched on vicarious learning about risk through others' trauma. The researchers in the study noted that family and associates of an individual who undergoes trauma experience comparable neurological changes to the original victim in sympathy. They theorized that vicarious learning is a survival mechanism, and that survival-based social learning in humans can occur almost by osmosis, driving the biological changes within the community. I found that fascinating!
