A precise quantification is not necessary to recognize the core point, that however you define interaction, you are in fact interacting with acquaintances much more than strangers. You don't need to put numbers on eye contact or anything like that. It's enough to go by e.g. physical unbarriered proximity.
>One possible explanation that has nothing to do with "interaction time" is simply the fact that you apply more countermeasures to strangers than you do to people you know. Perhaps the real cause is a matter of trust, not time.
That's saying the same thing: people apply more countermeasures to strangers because they (correctly!) recognize them as being more dangerous in the practically-relevant sense. After that filter is applied, and after swamping your interactions with acquaintances, the end result is a relatively low proportion of crimes from stranger-in-the-bushes. That doesn't mean predators in bushes aren't dangerous!
And, once someone has become trusted, they're no longer a stranger and likewise are less dangerous because they have more to lose from hurting you. Either way, by the appropriate metric, acquaintances/friends/family are less dangerous. The greater incidence comes from being around them more and from not using the same countermeasures.
Either way, it simply doesn't follow (as the OP suggested) that the rational thing to do is to be less wary of strangers!
Actually that's not my model; I'm not the OP. I was just pointing out what I saw as a flaw in your presentation. Y
You keep talking about things like "unit of interaction" - which is a handy thing to talk about in the abstract, but gives the impression that you've actually quantified human interaction - a concept I am highly skeptical of.
I can see that there is a reasoning flaw in looking at crime that has happened and seeing that it mostly happens between people who know each other and concluding that the greatest risk to yourself is from people you know.
One possible explanation that has nothing to do with "interaction time" is simply the fact that you apply more countermeasures to strangers than you do to people you know. Perhaps the real cause is a matter of trust, not time.