Christian> I would much rather receive and delete another annoying
Christian> proposition to get rich quick or see lurid pictures than tolerate
Christian> any form of censorship.
As has been pointed out, the non-member messages can be moderated. It takes
about one second to look at a message and tell whether it is unsolicited
commercial or not. So the downside is that the non-member message may be
delayed for a bit until the moderator gets to it. I wouldn't call that
censorship. (I think one has to be very privileged indeed to confuse a
small inconvenience with censorship.)
Unless, of course, you think that people have a RIGHT to send unsolicited
commercial email to IETF mailing lists.