I remember reading that the site started out in competition with The Saint, so "The Sinner" seemed like an apt title. (And "The Saint" is named after Saint Andrew, after which our town is named).
From my recollection the name started out as a pun on the newspaper's name, but the Saint at the time decided to take umbrage and started sniping at us for no apparent reason. It wasn't that the name was intended to be deliberately provocative, I don't think.