Can you be more specific on what you think the problem is?
I agree that the current (downvoting + minimum karma for Discussion) dynamic encourages creating new accounts, holding everything else equal. But I'm not sure what the downside of inflated registered-user numbers is - there's not much sock-puppetry locally, so it isn't clear how additional registrations can be considered relevant to signal-to-noise issues.
And there are tangible benefits to the downvoting system (helps increase quality posts, crowd-sourcing basic moderation).
It came to my attention that when you receive downvotes for your comments, your karma goes negative and you need to "pay back" to be able to post to Discussion or to Main.
Since new users start with zero karma, having negative karma seems to just encourage those with negative karma to create a new account. We don't want to encourage people to create superfluous accounts, do we? Therefore I think LessWrong codebase should be patched so that karma does not go below zero even with lots of downvotes.
What do you think?