I can answer your question on why there is a registry in spite of the factually low recidivism rate.
You’ve got these so-called “upstandin’ God-fearin’ Christian folk” who believe any amount of punishment short of lifetime (by this I mean until the day you die) imprisonment or execution is just not enough for someone who rapes a woman and especially for anyone who would molest a child. In their self-righteous indignation the public demands these laws and career politicians (who only care about staying in office) are only too glad to oblige these blood-thirsty monsters. Our politicians are not morally superior so as to be above this behavior! Just look at Mark Foley and Lester Wiener. Both pushed for the harshest sex offender laws possible all the while being sexual deviants themselves. Hypocrites!!!