As a general rule I don't downvote closed questions but I will do so if I see any reopen votes cast on a question that I think should remain closed, just to highlight the fact that it's a bad question.

Update:

After reading Ward's answer I have started to cast a few downvotes on closed questions, just to encourage them to disappear.

As a general rule I don't downvote closed questions but I will do so if I see any reopen votes cast on a question that I think should remain closed, just to highlight the fact that it's a bad question.

As a general rule I don't downvote closed questions but I will do so if I see any reopen votes cast on a question that I think should remain closed, just to highlight the fact that it's a bad question.

As a general rule I don't downvote closed questions but I will do so if I see any reopen votes cast on a question that I think should remain closed, just to highlight the fact that it's a bad question.

Update:

After reading Ward's answer I have started to cast a few downvotes on closed questions, just to encourage them to disappear.