Well, how many people do you think had sex last month (in a straightforward male-female coupling)?
It’s kind of hard to find good statistics, but wikipedia suggests that there were approximately 90,000 reported rapes in the United States in 2009. The FBI estimates that about 8% of these cases were “unfounded,” though this figure is not synonymous with “false.” Nonetheless, for kicks, let’s assume that all 8% represent false allegations of rape. That would mean that there were approximately 7,200 false allegations of rape in the United States in 2009.
So let’s see. There are about 300 million people in the US. Approximately 35% are either under 18 or over 65 years of age; while both of those groups contain a large number of sexually active people, I think the incidence of false rape accusations among the over 65 set is probably very small, and trying to figure out how many people under 18 are actually having sex is going to be difficult, so I am eliminating all of them (ie, roughly 105 million people). This leaves us with 195 million people between 18 and 35.
About 60% of these people are married, leaving us with 78 million singles. About 5-10% of them are gay, so let’s take the top end and cut out another 8 million. So 70 million heterosexual singles. Say 20 million of them are non-sexually active for one reason or another - priests, people in comas, people who just don’t enjoy sex, so on and so forth.
OK. So. about 50 million sexually active, heterosexual singles, which means roughly 25 million sexually active, heterosexual single men. If every one of those men has only one sexual partner in a given year, that’s still 25 million boinking sessions in that year. This is probably grossly underestimating the amount of man-on-woman sex happening each year, but go with it for the moment. This means that those 7200 false accusations of rape represent about three one hundreds of one percent of all sex.
So if you are a straight single man and you have a completely random hook-up with a woman, your chances of her making a false accusation of rape are about 1 in 3500.
Yup, I’m comfortable calling that “rare.” Particularly if you avoid dancing around the consent line and attempt to conduct the most basic screening for batshit crazy before getting horizontal. Those 7200 cases of false rape are terrible things, and despicable acts by the false accusers, but I think folks are over-stating the scope of the problem a bit.