I understand the need for a good, supported answer to prevent the site from devolving into a free-for-all battle of opinions. I even support this as a matter of personal preference (even though I'm guilty of some unsupported opinionated answers myself.)
However, some valid questions come up that cannot be answered with supporting Scripture because the answer is, quite literally, "There is no supporting scripture for that doctrine/statement/belief"".
This is a valid question, asked in good faith, and it is one that is looking for Scriptural basis for a specific doctrine. In short, it meets all of the guidelines for a good question, which can't be answered with a good, supported answer.
I answered this one to the best of my ability by looking for supporting evidence for the doctrine, and citing those that support the teaching, but the best I could do was point out that the support was lacking.
In the end, the lack of support made the answer seem like an opinion to me. I backed up my final answer with Scriptural reasons for why I found the doctrine to be Scripturally unsupportable, but even this felt empty.
What is the guideline for such questions? In this, I'm not asking if my answer on that question was correct, I'm asking if I took the proper approach to answering, and if not, is there a guideline that the community agrees on?
Another example: Is there a basis for Christian holidays in the Bible?