Information cannot be poisonous. Unless you trust it.
Laws about forbiding nazi and other extreme propaganda are in fact weakening the people, feeding them with only refined information. When they eventually get the propaganda (and you cannot stop copying of information), they will be unprepared and they will trust the information. This leads to grave results, as keeping humans away from infections weakens their immune system.
If introduced to bullshit gradually, human mind can learn to detect it and act accordingly, not accepting theories that have been proven wrong. So, if extremist propaganda is not banned at this point, no one would even care to listen to it.
The same goes about porn (and child porn). Thanks to adults' cult of sexuality, child's mind can see only its twisted form behind the taboos and if circumstances are unlucky, not see the true picture at all, bludgeoned by mindtraps. Later they can become rapists or child molesters due to unsatisfied urges.
If no part of body was tabooed, no one would care for porn, child porn, or any other kind of porn whatsoever. Well, in fact it would be like kissing scenes in films nowadays.
So, the key to strengthening the mental immunity is gradual increase in information amounts and severity. Four years old can be shown softcore porn and Communist propaganda, teenagers can watch hardcore and nazi proclamations, etc. It would be nice if there were studies in school, when children would be taught to find holes in logic of such statements. When achieving 18 years, such a person can safely aproach any kind of information and stay sane while assessning its true value.