The American origin story of the SOR, which was later copied in part by UK:  https://www.youtube.com/watch?v=wuKcInKFQPw

Also this person's channel describes the full force of the American system and offers mythbusting and advice for Americans moving to Germany (directed at Americas, although Britons with a particularly nasty case might take something from it).

It's only of academic interest to this UK forum, but illustrates that it could have been (or could become) a lot worse. 

Civil commitment mirrors IPP, in its lock em up and throw away the key approach to crime. The UK govt learned its lesson from that experiment.
I suppose the interesting question is why other countries rejected the idea of a register. Places like Norway, Switzerland and Finland all considered it and rejected the idea. But English speaking countries all copied the USA.

https://sage.cnpereading.com/doi/10.1177/17488958251356678