I just had a similar experience - I posted an (IMHO) well written question that was immediately downvoted with no comment. It has no answers because I suspect few people are going to look at a <0 question.
This upset me more than it should because in a vulnerable moment of need, I was digitally slapped. SO used to feel like a special gem of altruism where devs helped each other out for the love of it but now it feels like a faceless, cruel and nasty place that I want to avoid. I don't think we fully account for the emotional impact of such events when we introduce voting\karma type features.
Assuming for the sake of argument that the moderators were correct and my question was off-topic: it's really rude for half a dozen moderators to pile on and all say so. It gave the impression I was out of line / being told off and it really put me off continuing to be active on the website.
Getting down voted never feels good, but it sounds like the system worked exactly as it was supposed to in this case.
You might think "doh". But if you get down-voted, try deleting the post and post the exact same content twenty minutes later. You will be surprised.