Bullshit. Live in fear of strangers your whole life or trust the basic humanity of strangers. Either way you're still going to die of heart disease like the rest of us. Why don't you live in constant fear of that?
Stranger danger is a result of a fear-mongering media. Are you seriously worried about serial killers? Do you know how few of them there are and how freaking many people there are in the world?
People love to live in fear of things like strangers because it's immediate and controllable. They can just choose to stay away from them. It gives people a sense of control. Heart disease is long-term and amorphous. It's harder to gain immediate relief from fear of that.
By all means, don't leave a bunch of cash around while staying at a stranger's house. Take reasonable precautions. But fearing people by default is irrational.