Sexual assault victims should never have to been victims to begin with, but they bear those scars for life. And so should the people that inflicted such trauma. 

The registry serves to inform people of a potential threat (i.e., sex offender) in their neighborhood affording them to take additional precautions for their (e.g, spouse, children) safety. Given that victims have to live with the scars of sexual assault for the rest of their lives, it is reasonable that sex offenders also be publicly shamed by being publicly listed on the sex offender registry for life. 

I do agree that our definitions of "sex offender" need be narrowed so as not to include cases such as those involving young lovers ("of age" [18 y.o.] & underage [15 or 16 y.o.].