This question isn't really asking whether or not you should downvote answers on bad questions. This question is whether or not we should cut newcomers to the website slack when it comes to gray infractions. But to discuss the later, I need to discuss the former, and more specifically, how gray it is.
Is answering a bad question wrong? Yes, absolutely. This is a Q&A site with specific rules and one of those rules is that certain questions aren't allowed on this website. Answering such questions encourages this behavior. Thus, even if you can answer a question in full detail, if it breaks the rules of this site, you really shouldn't. Rules don't exist to be bent, they exist to be followed. Of course, though, these situations falls on a spectrum with a double axis - one axis is the question and the other is the answer. On the one side you have the extremes - a glaringly bad question and someone answering who is doing so in bad faith, i.e. said member knows he shouldn't be doing it. On the other hand, the other end is a question which is possibly a little too vague but you, in good faith, think you have an answer that works.
In the case of the former, I'm all for downvoting. It doesn't matter what your content is, if you're flagrantly breaking site rules in bad faith, a penalty is required to try and maintain order. I'm sure if a user does it repeatedly enough then the mods will step in and ban the user, but in the time being, I would argue that a downvote is justified. In the case of the later, than a downvote seems inappropriate - there was no bad faith and the user was justified in believing that site rules could be followed. Just vote to close and be on your way.
The gray area comes in the space between these extremes. If a question is sufficiently bad, is good faith enough of cover or should we say that at a certain point good faith can't protect you. On the other side, if you're answering a question you think is unsuitable, does the fact that it might actually be suitable save you? I think that can be a discussion for another time, but I would agree with The Daleks position in regards to new users - they just haven't had the time to experience the website yet. Certainly they should read the guidelines in the Help Center, but the guidelines are just that - guidelines. Veteran users of this site will have a much better feel for what is acceptable and what isn't.
Basically, the axis here, and consequently the gray area within it, should be expanded for the newcomers to the website. It's really not fair to hold them up to the standards of a veteran and we don't want to scare them away. Close down the question if it violates site rules, fine, but that's just a consequence. I don't think a penalty is in order unless we actually have reason to believe bad faith, and it's unfair to assume bad faith towards newcomers.