Because if someone is for instance, a thief, and he steals something from me, I can handle that. If someone is indecent with my child, it's more than just a "thing". If someone's out on parole from a murder sentence (not man-slaughter based on hitting someone while drunk, et cetera) then yes, I would kind of want to know what kind of danger I'm living near so I can move.
Why stop at sex offenders? I want a table-driven foodar that detects individuals who meet my filtering criteria and alerts me of their proximity as soon as possible.