I was kind of thinking about my voting policy which before I had not really thought too much about before, especially downvotes. What deserves a question downvote in my book?
After some thought, I concluded my basic policy (not perfectly implemented though, mea culpa) is to only downvote bad questions. Questions which are merely trivial or petty or easily answered are neither bad or good, so they get no vote. What would make a bad question (assuming it is on topic, etc)?
Loaded questions designed to start an argument, or interrogate people's political beliefs, rather than discover new historical information.
Incoherent questions. When I am having trouble figuring out what the guy is asking then the question must be bad, or at least its phrasing must be bad.
Unanswerable questions. There are some questions which are "answerable" enough that they are not off-topic, but at the end of the day are not likely to be answerable, like "What mental illness did Claudius have?" How are you going to even answer that? It's a bad question that does not really have an answer. I ask myself: lets say we evolve and become super-sentient. Will we EVER be able to answer this question? If the answer is "probably not", the question fails the test.
Questions based on incorrect or unproven assumptions or premises. I hate these.
Maybe other people have good criteria for voting a question up or down.