Actually, according to Burrows, Abadi, and Needham "A Logic of
Authentication,"
a digital signature indicates that you "once said" those words. It doesn't
say anything about when you said them, or, more important, whether you would
still say them in the present. This is not academic - especially if I'm going
to take some irrevocable action based on what I believe you believe.
There's no conflict here. The semantics that "having said" something in an
irrevocable way are not at issue. If you send out a signed object you did in
fact "say" whatever is in that object. The question is instead whether or not
others can assume that what you "said" is in fact your actual position on an
issue or whatever. In the case of a text/plain object there's little issue --
it nominally contains words you authored (unless otherwise indicated by the
context). However, as I said before, the act of forwarding and signing a
message should not be construed as endorsement of whatever the message
contains.
Ned