Let me expand a bit on my reasoning:
Currently the email addresses are available on the memberlist page. Anyone can copy and paste those addresses and send email
( or extract them using a web robot )
anouncing products, stuff forsale etc.
Now I don't personally think that's a good thing to do, but since there is no restriction on someone doing it currently, might as well suggest some form of consideration in support of the site for it's use.
OTOH, the membership list could not be public. Or, maybe there's an "opt-in", "opt-out" option for memebrs, but I imagine that would ba a PIA to administer.
I hope that made some sense, it might not have.
DaveH