Because if JKR isn't planning the tiniest whiff of a S&W reversal (which, remember, does not entail somebody suddenly turning good but just readers being led astray in assigning guilt for specific crimes) she's certainly done a damn good job setting up for one.

I'd have a much easier time believing that she's doing that deliberately if I hadn't read her interviews. Whether she's going to have a plot twist or not - I really dislike being hit over the head with her "no, don't expect a plot twist, how dare you even suggest such a thing!" talk.