Both of those definitely changed; unlike some of the other things you say, this is not ridiculous. However, I can easily imagine finding in, say, the personal correspondence of Archimedes, a statement like "this idiot tried to show me another squaring-the-circle proof again". We do preserve personal correspondence in ancient records, and that sort of thing doesn't require a lot of access.
> No harm in being wrong on the internet.
http://www.mamapedia.com/article/mmr-vaccination
Money quote: "I have really close friends who swear that within 24 hours of the MMR their child had symptoms of autism"
> Politeness is more important than rightness as a rule to enforce.
It's better to be right. Enforcement of politeness greatly retards, and can prevent, the discovery / acknowledgement of rightness.
> Rightness sorts itself out among able and interested parties.
This can be tautologically true, depending on your definition of "able". It's very clear that rightness does not sort itself out among interested parties, and they can be harmed thereby.