Quality is a serious issue. Addressing the quality of our questions and answers is, I'd argue, the primary issue for our site right now.
However, unregistered users may not be the right place to look. What does it for a user to be unregistered? All it means is that that user has no OpenID associated with their account. This doesn't mean their posts will necessarily be of low quality.
In the case of this particular user, I'll grant that their contributions haven't been the best so far, but it's our job to nudge them in the right direction. Account removal is reserved for very serious and specific issues that cannot possibly be addressed in any other way. Users who are here in good faith aren't going to have their accounts vanish suddenly (imagine the situation in reverse).
So, the question is, how do we manage this content? And it does come back to community moderation. Moderators are here as exception-handlers; when things aren't going the way they should, and someone needs to step in to nudge it back in the right direction. We're not here to monitor voting on questions and to close them, except occasionally.
You all, the users of this site, have two tools: voting, and close votes. Use them. I'll take as an example this question, which had, for seven hours, this comment:
There is a way too many correct answers to this one unless the person who wrote it wont accept anything that would obviously work.
It had four upvotes when I closed the question. There were only two close votes on the question itself. This meant that there was clear consensus people thought the question should be closed, but only two people actually decided to take action about it. The question still sits at +7/-4.
Here's another question that has 23 answers, isn't well-defined, and still only has three close votes. In my opinion, this should be absolutely closed, but it hasn't been. I am honestly not sure why.
When you see a bad question, or a bad answer, downvote it. Our sitewide upvote/downvote ratios are terrible right now. We're not using our downvotes. Start using 'em. They're good for the site.
These are the primary tools we use to guide new users. We're not going to delete them when it's clear they're here in good faith and mean well to the community. Instead, we set a precedent that we don't like this content by voting it down and voting to close it where applicable. Both the good and the bad are helpful in narrowing our site scope.