http://en.wikipedia.org/wiki/Reactance_(psychology)
Reactance occurs when a person feels that someone or something is taking away his or her choices or limiting the range of alternatives.
Reactances can occur when someone is heavily pressured to accept a certain view or attitude. Reactance can cause the person to adopt or strengthen a view or attitude that is contrary to what was intended, and also increases resistance to persuasion. People using reverse psychology are playing on at least an informal awareness of reactance, attempting to influence someone to choose the opposite of what they request.
It is assumed that if a person's behavioral freedom is threatened or reduced, they become motivationally aroused. The fear of loss of further freedoms can spark this arousal and motivate them to re-establish the threatened freedom.
When certain free behaviors are threatened or removed, the more important a free behavior is to a certain individual the greater the magnitude of the reactance.
Silvia's 2005 study concluded that one way to increase the activity of a threatened freedom is to censor it, or provide a threatening message toward the activity. In turn a "boomerang effect" occurs, in which people choose forbidden alternatives.
during the reactance experience one tends to have hostile or aggressive feelings, often aimed more at the source of a threatening message than at the message itself.
I would say this is why a lot of political policy often has the opposite of the intended effect. If I'm going to try to prevent you from holding a Nazi rally, then it makes you want to hold a Nazi rally even more. If I successfully stop you from attacking someone, it doesn't turn you into a good person - it just makes you look for a chance to attack that person when I'm not around.
This isn't to say that nobody should try to stop murders. Yes, by all means, stop murders, but what many policy makers seem to fail to understand is that they are only fighting the symptoms, without working on a cure. In response to fascist ideology, I'd probably divide response into two types: short-term and long-term. Short-term response is the practical one - yes, you want to stop attacks on Jews, immigrants, or other minorities - but do realize short-term responses often result in reactance. Long-term responses look at the underlying causes - sure we can try to stop people from killing each other everyday, but what causes people to try to kill each other in the first place?
Whether it's "terrorism" or Nazi ideology, if you want your targets to listen to what you say, you in fact should *not* disagree with them - or at least your arguments should not be presented in such a way that makes them feel bad about themselves. Whether you like them or not, you have to at least pretend to be on their side, even if you want to wring their necks. This is for long term behavior modification only - obviously if they're in the middle of actively assaulting someone, pretending to be their friend is going to have to go out the window. In any case, to affect long term behavior, it's easier to avoid reactance by slowly nudging them in slightly different directions, rather than trying to force a large course correction - ie. do they really hate immigrants because they're smelly, or are they just frustrated with their economic outlook? If you attempt to take them head on, and try to argue that immigrants are actually very clean, it usually just makes them dig in their heels, especially if they fear public humiliation. On the other hand, if instead of attacking immigrants, they could more practically improve their economic situation by doing X, then eventually they may stop thinking about immigrants altogether.