It is a question, an open question intended to provoke debate and teach about a subject, in effect it's a request for an FAQ. Now perhaps SO is not intended to be for that sort of question, and that is of course for SO to decide.
I suppose the reason many people come to SO to read questions is that they'd like to learn about a subject area, and the reason many people come is write answers is that they'd like to teach a little about a subject, and this sort of open-ended questions offer the opportunity for someone to answer questions the asker didn't even know they had - like should I add an index to my db, if so when? Should I use natural keys? etc. To in effect tell them to unask all those questions they would otherwise have asked in groping their way to familiarity with the subject. It functions as an FAQ for that particular subject, to prevent beginners from making the same mistakes/asking the same questions over and over.
So that sort of question can be very useful for someone starting out, for the kind of person your site targets. Maybe that sort of question belongs on some other site though, a sort of training site rather than a question/answer site, or maybe SO should just expand to encompass that sort of FAQ function?
I'm not so convinced that for this category of question there is a clear line between 'db x breaks when I do y, what should I do?', 'Do I need to use db transactions in db x?', and 'What are the common db mistakes?', and that one sort of question/answer is rational, and another narrative - is the division really that clear? Are there not many many borderline questions which solicit opinion (of someone who knows more about the subject), and yet are useful for others too? Are not many of these smaller 'science-in-the-small' questions actually answerable in many different ways, each of which may be somewhat valid and none of which is actually 'right' in some categorical way?
For example this question, which is equally open-ended, remains open (rightly so I think as it could be a useful discussion :)
http://stackoverflow.com/questions/327199/what-will-we-do-af...