[harimau777]

I think it's somewhat more complicated than that.

Traditionally there was more friction to speech. I don't even mean just that the average person doesn't have access to a national platform like CNN. Even something like mailing out fliers had non-trivial costs. It's the same reason why junk mail is generally less of an issue than email spam.

In a traditional town square, people are not anonymous and the "square" was local enough for there to be social consequences to actions. On Twitter, many of the posters are anonymous and even those who aren't often live on the other side of the country.