a sociopath posting on an alternate account to avoid the social consequences of holding such a stance?
There are easier ways to avoid the social consequences of holding said stance; one of them is to denounce that stance. Another is to fail to comment on the matter. Logging in to an alternate account in order to say something they don't want to be seen saying has a small prior to begin with.
p(Author is a sociopath | Author chose to RP as Voldemort specifically) > p(Author is a sociopath | Author went with a different pseudonym) is my basic assertion here. People who roleplay sociopaths are more likely to be sociopaths - roleplaying Voldemort is a safe outlet for that tendency.
That the author is writing Voldemort also seems like evidence for the hypothesis that the author agrees with Voldemort (I'd assume possibly not to that extreme, but who knows). Much the same as everyone assumes that the author behind shokwave agrees with shokwave's writing...
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: