How Did Voldemort Do It?
Have you ever wondered how Bellatrix Lestrange and the other Death Eaters became so enamoured with Voldemort? I mean sure, they were probably somewhat unhinged and may have even been pure evil, but what lead Malfoy, Crabbe, McNair, and Barty Crouch Jr to don scary masks and kill people? They knew society frowned upon it (hence the cloaks and masks) but how did Tom convince them to kill, torture and maim people anyway? Probably not by advertising free hugs…
Lord Voldemort used a fair few persuasive techniques (other than the Imperious Curse, of course). The most notable technique he employed was the ingroup/outgroup technique, in which he created in groups of wizards against muggles. Within the wizard ingroup, he created more circles of in-groups: purebloods vs half-bloods and muggle-borns, death eaters vs everyone else. Within the ingroup/outgroup technique, Voldemort intertwined similarity and the power of authority pressure to get people to do his bidding.
The ingroup/outgroup technique is responsible for innumerable instances of persuasion. So, how does it work? A meta-analysis by Bettencourt, Dorr, Charlton and Hume (2001) investigated the effect of high or low status on in-group/outgroup biases. In Voldemort’s case, the high status group would be pure-bloods, and the low status group would be half-bloods or muggle-borns. The meta-analysis showed that members of high status groups showed stronger biases: they viewed the in group to which they belonged as more positive and the corresponding outgroup significantly more negatively. Low status groups showed the same biases, but to a weaker degree. I.e. the muggle-borns and half-bloods were less biased against the pure-bloods than were the pure-bloods against the muggle-borns and half-bloods (the pure-bloods were meaner). The study also shows that members of high status groups (the pure-bloods) identify better and more easily with other members of their group than members of low-status groups do (the half-bloods and muggle-borns).
The table above shows the effect of perceived vs real status differences, and the effect that these have on ingroup/outgroup biases both between and within groups.
Voldemort was able to successful persuade people to kill each other, to terrify other people into killing each other, and to hunt a 17 year old boy mercilessly because of how well he convinced people of the ingroup/outgroup divide. Both groups identified with either their high or low status, and that created a shift in the perception of power and strength; instead members of both groups realising they were as powerful as each other, the high status groups believed they were more powerful, a more legitimate authority. Their conviction in such beliefs allowed for the ingroup/outgroup divide to grow stronger and to start insidiously convincing the low status group (muggle-borns, half-bloods) that they had less power to yield, making them more vulnerable to persecution.
Status differences and in-group bias: A meta-analytic examination of the effects of status stability, status legitimacy, and group permeability (2001). Bettencourt, B. Ann; Charlton, Kelly; Dorr, Nancy; Hume, Deborah L. Psychological Bulletin 12, 4 520-542.