I’m not going to discuss the merits of the rules, but postal mail seems a terrible comparison to the web. Global visibility, instant transmission of ideas, effectively free (as in beer) distribution.
Yeah, I think this is one of those domains where frictions (or lack thereof) matter. It is much faster, cheaper, and easier to send out a significant volume of material on the Internet than through the mail. In theory, somebody could send a bunch of obscene trolling letters, but having to lick all those envelopes seems to deter most of the people who'd be otherwise tempted.