If the attacker is willing to put work into spamming this specific site, which is possible, then neither of these gets us anywhere, since you don't need karma to give karma. To be an effective barrier, you would also need to limit voting to those with positive karma. I'd support that.
EDIT: Admins would then have to track down and delete those accounts which gave positive karma to spammers.
If the attacker is willing to put work into spamming this specific site [...]
Which is far from being certain, and so worth testing in this obvious way.
Spam (curiously enough, always for jewelry) accounts for maybe two-thirds of what comes through the LW Discussion area's RSS feed these days. So although the moderators have been doing a great job of quickly removing it from the site itself, it remains a substantial annoyance for those of us who keep track of LW through a feed.
I think it's time to revisit the possibility of making it harder for people to post in the discussion area. Clearly it would suffice to limit posting privileges to those who have a positive karma balance. If that seems too draconian, as it did to some people in the previous thread, it would probably be enough to limit posting privileges to those who have ever received a single upvote on any comment they have ever posted.
Would any administrator care to undertake this? If so, many thanks.
(My apologies if an unfinished version of this post briefly appeared on the site some hours ago.)