Most if not all questions that requires closing are need to be closed for obvious reasons.
If I say most is because some duplicates are questionable and up to discussion about if they are a duplicate or not. But when it comes to on/off topic, too broad etc.. It is pretty much always obvious on first sight.
Why do we need 5 votes to close these questions. I'm not talking about a single click to close system but why not dropping it to 3 at least? This would greatly lighten the work charge in the close vote queue by pretty much 40%. The main security when closing questions it the fact that users cannot vote before acquiring 3000 rep+. By then, these users are usually capable of knowing what questions belongs on this site. 3 of them would be more then enough to tell a question needs to be closed.
Try finding a post with 3 close votes that shouldn't be closed.