Oh it has happened. Nick Holbert who was a registrant murdered (no sexual assault) Kelli Bordeaux in NC. Basically he was out on a date/drinking with her and someone told her he was a rso. She started acting distant with him and when he took her home she went off on him calling him a child molester etc and he beat her to death. The question is did he go off the deep end because of the registry or was he one of the bad ones that make us all look bad.
If you are talking about registrants becoming radicalized or extremists I don’t know, but when you take everything away from someone that makes them a person anything is possible. The registry certainly could create the right environment for that kind of behavior. From everything I have seen and read the registry increases the likelihood of someone on it creating any crime and mostly non sexual with factors like homelessness, anger, fear, frustration, stress, isolation, no social or family structure etc all playing a part.