I'd first like to applaud THelper for going with the democratic majority, despite the small sample size. I would like to have seen this done elsewhere (e.g. with this question).
That said, in general I think that if 3 people wanted to close the question, and 2 wanted it open, or if 30 wanted to close it, and 20 wanted it open, it still should be kept open.
A simple majority should not be sufficient to close a question. I find it absurd that Stack Exchange lets one moderator, or 5 users close a question, regardless of how many people have viewed, and or voted up the question.
Close a question if it's clearly harming the site. If not, leave it open and let the userbase decide. If you don't find the question useful or interesting, don't answer it. The existence of an imperfect question on a site you participate in is not stopping you from participating in the other questions you do find useful.
However, when you close someone's question, you are stopping their participation. Period. There's not a symmetrical effect to closing vs. leaving open. Therefore, I think it would be entirely appropriate to demand a higher level of support for closing a question. One moderator, or five users, is far too low a bar.
I remember reading a question once on meta.stackoverflow.com once that basically identified that 5 out of the 10 most popular (votes, or views, I can't remember) questions of all time on Stack Overflow were currently closed. To me, this is irrefutable evidence that the site's priorities are backwards, in this regard.
Beauty is in the eye of the beholder, and if a sizable number of site viewers find the question useful, then it's useful.
I would also reject any "slippery slope" arguments concerning the hypothetical possibility of the site turning into a free-for-all, overrun by people asking questions only about fringe sustainability topics. One, we're not there, or even close. The site's traffic is still very manageable, and virtually every time I look at the review queues, they've been completely drained. We don't have a problem with trash on the site (and there wasn't, even before we had moderators pro tem). Two, this is sustainability. It's a low volume topic, for better or worse.
I acknowledge that on busier sites, like Stack Overflow, the balance changes a bit. But, we're not them.
I also acknowledge that my view on this greatly conflicts with the majority of SE moderators, and power users, and accept getting downvoted into oblivion. However, sites like meta.stackoverflow.com have turned into an echo chamber of a very small percentage (~1%) of overall site users recycling (no pun intended) the same opinions on site policy. I hope this site doesn't turn into that.