It's not funny

I have always wondered about the "loud/excessive laughter" clause of Mormonism. I understand the principle of avoiding light-mindedness because too much levity could eventually lead to not being serious or passionate about anything. But loud laughter? Surely it's not the kind of sin that keeps you from getting to Heaven. And our prophets and general authorities have often talked about humor (more often than not in the context of marriage, interestingly enough).


So what's the deal with laughter?


I remember that a religion teacher at BYU once said that in the scriptures the word laughter was never used in a positive context, as in: 


"for the devil laugheth, and his angels rejoice, because of the slain of the fair sons and daughters of my people; and it is because of their iniquity and abominations that they are fallen!" (3 Nephi 9:2)


or 


"And he beheld Satan; and he had a great chain in his hand, and it veiled the whole face of the earth with darkness; and he looked up and laughed, and his angels rejoiced." (Moses 7:26)


Just warms the soul, doesn't it...


But other entries in the Topical Guide are not as gloomy and in many instances the words laughter and rejoicing are used interchangeably. That still doesn't answer my question though. D&C 88 says "cast away your idle thoughts and your excess of laughter far from you."


But what exactly makes this such a big deal?


I found that this talk by Peter B. Rawlins entitled "A Serious Look at Humor" was very helpful.


What are your thoughts on the matter?