Folk Islam refers to particular flavours of Islam that are practiced in various parts of the world. For example, muslims in the Indian Subcontinent have absorbed many aspects of cultural folklore and beliefs into their own practice of Islam; despite having little to no true Islamic basis, the line between culture and Islam may not be very well-defined by the populace at large. Such cultural flavours of Islam are rarely seen anywhere else (unless there's a large immigrant population).
For example, the following questions seem (to me) to touch on issues more cultural than Islamic:
- Is the practice of “melting lead and pouring it into cold water over the head” from Islam? (meta)
- Is it okay to whistle after maghrib?
While I believe that asking whether such practices have an Islamic basis is fine (there is now an islamic-basis tag for these cases), that's a fairly strict line, especially when you consider that such practices are often considered "Islam" by the practitioners thereof (or by observers of the same community).
It must also be noted that it may be difficult if not impossible to know in advance whether such are actually cultural rather than doctrinal; a lack of evidence is not the same as proving a negative. And expecting all users to prove that a practice is Islamic before asking about it is probably not a viable strategy.
Keeping these points in mind, to what extent should such questions be allowed? Should, for example, questions asking about the practices themselves, or for practitioners to provide evidence supporting them thus ever be appropriate?