Counter to that, Italy has a provision in its Constitution that forbids the reconstitution of the fascist party and now we have at least two that declare themselves as such (and have a few seats in the parliament), and one that, despite not being explicitly fascist, has more or less similar ideals and methods, has the relative majority of consensus in the country and is governing right now.
EDIT: did I write something false, inflammatory or off topic?
is that a counter point, or just an example of Italy's government being impotent? if it were china, the members of those parties would all be dead already
Nor have they taken over in any other country, regardless of being banned. Because their ideology has already been exposed for the bullshit it is. The ban did nothing.
Both Reddit and YouTube are general purpose sites. Very, very few people go on there to discuss the e.g. racist beliefs they already have. But the algorithms on these sites ends up exposing people to extreme views - there are many, many examples out there of people watching an innocuous video on YouTube only to immediately suggested a 9/11 conspiracy video or a barely concealed white supremacist tirade.
If that content were removed from YouTube and Reddit people wouldn't be going underground for it, because they wouldn't be looking for it.
(and as a more general thought, invoking Nazis here isn't all that useful. Just because X had Y effect once in history doesn't mean it will every time. Germany has outlawed Nazis since the end of WW2 and guess what... they haven't taken over again.)