In our pursuit of great answers, we seem to have forgotten that even good questions can start out a little rough, or even very rough.
Downvotes are very common, and based on the comments following in their wake, they seem to discourage people asking questions more than encouraging them to improve their questions. This issue has been addressed many times here before, one of the best suggested solutions I've seen here is: How to defend new users from unconstructive downvoting
In that post Clockwork suggests requiring comments justifying a downvote. I think that because the normal posters here on SU tend to be less tech-savvy on average than those found SE or SF, for instance, we need to be at least as welcoming as they are. As I understand it, SE requires a justifying comment on a downvote, we should too.
But another issue is the cheapness of the downvote for the person actually doing the downvote. While Clockwork tried addressing the weight of a downvote to the person receiving it, I think the downvote ought to cost more to the person giving it.
Finally, while there are scripts in place that check serial downvoting, as I understand it, these are triggered based on the number of downvotes received by a specific user, not by the number given out by a specific user.
We should be encouraging engagement and improvement rather than drive-by cheap downvoting, and I believe the solution is a combination of all three of these:
Downvotes should cost more to the person giving them. This will encourage conviction that the question is actually bad enough to be worth sacrificing X amount of your points to.
Downvotes should require justification with the intent of improvement. This will force engagement and improvement rather than the casual snobbery they currently embody.
Downvotes should be limited per account per day, just like close votes. For a young questioner, a downvote can be as discouraging as a close vote, and usually come with less accompanying information. Limiting the number of these that can be given out will also encourage people to engage with what they consider poor questions in a more proactive way.