In 2006, approximately 49% of violent crimes were not reported to police. Being the victim of sexual assault is expensive; each incident imposes an external cost of over $100k on the victim. However, recent estimates of the total social cost are an order of magnitude larger suggesting that from a social welfare standpoint rape is likely to be underreported if the victim’s demand for reporting is price elastic.
Please excuse the jargon. The old adage that "what you tax, you get less of" is what this is saying. We can't both yell at victims to report crimes against them, and slam them with the costs for doing so. It's hard enough to report, given common feelings of societal betrayal.