We want to be able to provide the means for whistleblowers and others to communicate in a secure and anonymous fashion. Yet we need to make sure we're not abused too much since sooner or later laws will catch up with the remailers should abuse sky-rocket.
The ratio of remailer use to abuse is painfully low because there's no way to actually communicate. You can broadcast but not recieve, because no system exists to receive mail psuedononymously. This is not communication. Remailer use is restricted to when senders don't care about listenerssss, which means rants, death threats, and the abuse of spam. The only systems for receiving mail are at best some college student's unimplemented thesis. Let's take our shining example of truth and freedom, the whistle-blower. When they send out mail to the media or whomever, one of two things happens: they see the story published or they don't. If not, there's no idea why: was it received? Did the media want more information? Did they need more support? Do they want to verify it? Do they want to help the whistle-blower? Even if the story is published, whistle-blowing is kneecapped: it can't be supported, or expanded on, or debated in any but the most rudimentary fashion. It doesn't matter if remailers disappear, they've already failed.