When men talk about “sluts” they are typically not referring to the number but a behavior. Imagine a woman who wears revealing clothing, is loud, engaged in conversations about sexual subjects all of the time, goes to clubs/parties and allows men to touch her constantly- except there would be one caveat, she is a virgin(has never had penetrating sex or given oral sex) thus equating to an N-count of zero. N-count is just a proxy men use to justify this, but has no actual measurable bearing on the attitude they would have towards this woman. N-count appears to be a proxy for being a “slut” and not the actual measure of it.

This woman in my example would be considered a “slut” by most standards and a man would have a good reason for not dating this woman, similar to how an employer would not want to hire someone who dresses sloppily and is always late for appointments. Is it fair to say a man would be “insecure” for not wanting a relationship for this woman, yes because there is little confident this woman would behave herself in a way that is expected in a relationship, again to give the same example an employer would be “insecure”(as in not confident or assured) in hiring the slob with a tardiness issue.

This is not to say that woman who behave in the way the woman in the example does are undateable, she could in fact only act like that out of a relationship, just as some people could be like the potential employee in the other example but once you hire them they change their behavior. But the idea of being “insecure” about dating a “slut” seems perfectly rational and the point has little do with N-count(even though an N-count of 100 would bring up some questions).