The close/reopen voting system has an asymmetry that promotes closure wars on meta and is vulnerable to abuse.
Once the first vote to close is cast, the matter of a question's survival is raised for a vote. But it is a one-sided vote. Only those who support one side of the matter can express an opinion. Once a question is closed this of course biases the vote on re-opening, as some people who would have originally voted to retain the question (had that option been available), may not want to promote closure wars. Also, after closure, fewer people will see the question, especially those who saw it while open and did not know there is any vote in progress.
Several recent closed questions were reopened, after the matter of closure had consumed much time on the meta. This indicates that, had the voting options been "close" and "keep open", either keeping open would have won outright, or the number of close votes minus open votes may not have reached as high as five. Thus, several of the closure wars would have been avoided had the voting system been more expressive.
As the user population grows, a closure system that requires a small fixed number of votes to close a question can be abused through the presence of a sufficient number of hard-liners acting individually or in concert (e.g., at present, five grammar pedants would suffice to close any question with a syntactically incorrect title). This would be much more difficult in a bipartisan voting system that allowed both Close and Keep Open as options.
A bipartisan voting system would offer:
-more certainty (or at least, a higher chance) that outcomes reflect a consensus
-less conflict on meta
-less potential for abuse.
Offered for discussion before adding a [bug] tag.