There was nothing stopping people emailing the manifesto to each other privately using any archive formats. That is different from having to provide a free soapbox for supporters of the manifesto. Just as you have the right to block someone commenting on your Twitter posts. The ISPs are businesses and have legal terms and conditions to remove anything. That is not censorship. Here in NZ it became illegal to transfer the manifesto, but primarily the video which was deemed offensive under existing censor laws.
> "The laws against "gay propaganda" in Russia are similarly supported by the majority of the population, but they're no less wrong and oppressive for that."
If the Russian example you give is supported by the majority then that is by definition democratic, even though propaganda created that public sentiment in the first place. Should propaganda (manifestos of hate in this case) be censored? Your own example suggests "yes it should".