I personally thought the question was unanswerable. It seemed to difficult to include diabetes at all, and didn't expect anyone would do more than stating that laughing won't cure diabetes.
Yet Chris included a stunning amount of references and links to online copies of those references and wrote an extensive answer, which really will make all future questions regarding laughing duplicates, because every aspect has been included in this answer.
Furthermore, the answer inspired this Meta Thread!
The great part about this answer is that it actually doesn't support either side, but concludes that there is no objectivity in the research done so far.
And then it goes on to prove beyond doubt that no consensus can be reached regarding this matter, because the data collected is insufficient.