I agree with Mr_Green's statement with just one modification:
When you know for sure that what a person has stated is correct, but doesn't have cited a source, then also you should up vote the answer.
And how can you be sure whether he has written the correct thing? It can be because, you may have read or heard it somewhere before from a reliable source or you know it from you personal experience. When you know something is correct and valid, then do up vote. For example, I up voted the following answer:
There the user doesn't mention any sources, but I know he has written the correct things relevant to the question. There is another answer (Sid's) to that same question which also mentions the correct thing, but I have not up voted that answer. It is because, I have forgotten how to determine the Ishta deva from birth chart. I know his answer points to the right direction, but I am not completely sure whether the user provided this answer having some prior experience or just copied from the source. Because I am myself not sure of the solution I have not up voted it yet, but I'll do so when I come to know the method again from the source I had learned. So I stayed neutral there. But the information was useful and new for the OP and other users so they casted their vote.
So the point is, If for any reason you know something is correct and valid, then do up vote even if it doesn't have any sources. But if you are not sure, then just stay neutral. If however, you were not sure and the answer provided some information that was useful to you, then also do up vote.
NOT EVERYTHING IS PRESENT IN THE SCRIPTURES
Due to freedom of people's thinking they can have lots of doubts and can ask different sorts of questions. But all the answers can not be found in the scriptures. For example, in the Bhagavatam it says, while Kamsa was driving the chariot of Vasudeva and Devaki, a voice from an unembodied source addressed Kamsa and told about his future death by the 8th son of Devaki. Now a person may ask,
"We see many times in TV, and epics that someone from the sky foretells and warns about things. So who is this guy? Is he the god? And why he chooses to show up at certain times and not always?"
Now what answer one would give to that? Scripture just says aśarīravāk - a voice from an unembodied being. It doesn't say any name, place, reason, etc. So how can one answer such a question as per the scripture?
So there are at least these three kinds of Questions:
- Whose answers are publicly available in the scriptures.
- Whose answers are not available in the scriptures, but are present in the mind of a teacher.
- Third are useless ones, whose answers can not be given by Brahma himself! But some people would certainly cast their opinion to show off their knowledge. So the third ones are opinion based questions.
So it would be incorrect to expect that everything can be answered as per the scriptures. But for stories and epics, the scriptures are the authority. Because it is from puranas and epics that most of the stories emerge.
Blog or Scripture, Which should be given more value?
Of course scriptures. But blogs are also accepted when the blog posts are based upon scriptures and provide proper reference. But posting blog based answers show little or mostly zero research attempt. The answerer should open the referenced scripture and verify if what's in the blog is also present in the scripture. Because most times, that's not the case. People just mention scripture names to sound authentic. So when multiple answers are present in which one is based upon scripture and one is beased upon blog post, the former should be given weightage by up voting and the later should be left neutral.
VOTING IS SUBJECTIVE
People can have different criteria for what they consider as a good answer. As I have previously stated, unlike a coding answer, not all the answers can be checked and verified for their correctness when it comes to religion; especially indirect questions, straight answers of which are not present in the scriptures. Even if you provide a straight answer, people may not accept it because they have different criteria in their minds. For example, consider the following answer:
Krishna(the user) accepted the answer not because I provided a scriptural reference, but only because of a line that was told to me by a saint. So even if I had answered that line only, without quoting the straight answer from the scripture, he would probably have accepted that too.
So because these things are subjective we can't expect everyone will behave the same. But, if quality is what we want here and not just quantity, then more weightage has to be given to answers that are based upon scriptures and reliable sources. Otherwise any tom,dick and harry would shower their opinion and make it just another site on the Internet. So let that be the uniqueness of this site.
However, because all might not have read and studied scriptures and because all answers might not be possible through scriptures, we should not discourage them from participating by down voting their answers. Backing up answers is good, but it can not be expected from all and always. So we should stay neutral to such answers unless his intention is something different and his answer contains wrong information. But if answers that are based on scriptures and provide reliable references get drowned by wrong and unreliable answers, then we can certainly down vote such questions to give weight age to the correct one.
The best thing to do is yo decide which questions are opinion based, and close them down to minimize opinion based answers and encourage scripture based correct answers by up voting them and staying neutral to seemingly correct but un-backed up answers.