My buddy was 18 when he slept with his 16 year old girlfriend. Her parents disaproved of him because he was the stereotypical trouble maker during his time in high school. He fit the "stoner" grunge image perfectly. He was not allowed to enlist in the navy. He cannot own a gun and has to register as a sex offender. He still gets harassed on occasion due to the fact that he manages a store in a popular mall. The sex offender system really needs to be reformed.
The ubiquitous 16 and 18 year old relationship is not a sex offense in most states in the U.S., there are some exceptions though. Most of the United States list the age of consent at 16, others often make allowances for a disparity of age, for example its only a crime if you are more than three years older than the person who is under 18, and a few states have a hard and fast under-18 rule. This fact alone indicates a big problem. For example, the quoted relationship would be illegal in Arizona, a person convicted of this offense in Arizona would have to register as a sex offender if they move to Washington, despite the fact that the crime that they commited in Arizona is not even a crime in Washington. That alone is enough to call the whole registry into question on it's face.