The need to create a new account is a trivial inconvenience that makes it slightly less likely that the person in question will stick around. And people with negative karma are probably ones that we, on average, would prefer not to stick around. Your proposed patch would make it more likely that they did stay and remained active.
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?