What makes you so certain that the Voldemort post was a joke, and not simply a sociopath posting on an alternate account to avoid the social consequences of holding such a stance? Certainly, there seem to be quite a few other people here who would pick immortality over saving 28 other lives, if you put the two choices "side by side".
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.
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: