The potential cost there is that there are occasionally some really bad posts that deserve the rapid downvote—such as those that don’t respect important Forum norms, even if not quite to the point of formal moderator action. In those cases, the hail of downvotes allows the Forum to deal with those quickly and without moderator action that could be seen as “censoring” someone. But maybe those kinds of posts are rare enough to incur the cost.
The potential cost there is that there are occasionally some really bad posts that deserve the rapid downvote—such as those that don’t respect important Forum norms, even if not quite to the point of formal moderator action. In those cases, the hail of downvotes allows the Forum to deal with those quickly and without moderator action that could be seen as “censoring” someone. But maybe those kinds of posts are rare enough to incur the cost.