They're completely unrelated examples. I'll try to explain why.
Iran's (authoritarian, human-rights-abusing) government wants to prevent citizens from communicating with each other using tools that are resistant to interception by their secret police. HN supports the basic human right to privacy, and thus wants to help Iranians circumvent unjust laws or government actions.
White supremacists (who happen to support Trump, because duh) are being banned by Twitter -- a company, notably distinct from a government, and thus incapable of "censoring" anything. This prevents them from using Twitter's platform to publish hate speech and (arguably illegal, definitely unjust) calls to violence. HN supports the right of a company to decide who can publish content on their platform and agrees that it's cool to tell racists that they aren't welcome there.
Iran's (authoritarian, human-rights-abusing) government wants to prevent citizens from communicating with each other using tools that are resistant to interception by their secret police. HN supports the basic human right to privacy, and thus wants to help Iranians circumvent unjust laws or government actions.
White supremacists (who happen to support Trump, because duh) are being banned by Twitter -- a company, notably distinct from a government, and thus incapable of "censoring" anything. This prevents them from using Twitter's platform to publish hate speech and (arguably illegal, definitely unjust) calls to violence. HN supports the right of a company to decide who can publish content on their platform and agrees that it's cool to tell racists that they aren't welcome there.