Do rape shield laws provide a good way to address the problem of underreporting sex crimes?
I would argue that rape shield laws provide an important, but incomplete, way to address the problem of underreporting of sex crimes. There would surely be more unreported crimes without such laws, but the laws do not completely prevent underreporting.
Rape shield laws do help encourage women to come forward and report crimes because they protect women from having their sexual history become an issue during a trial. This spares women from being grilled in court about their past. However, these laws cannot prevent the media, for example, from discussing a woman's sexual history. This would be an embarassing thing and is likely to deter women from reporting crimes. Rape shield laws also do not protect women from the possibility of retaliation if they report that they have been raped by an acquaintance.
For these reasons, rape shield laws are important, but they do not completely solve the problem of underreporting of sex crimes.