Understanding the dispute between Rashi and Kallah Rabbasi on singing Song of Songs?
Sanhedrin 101a.2 teaches:
תנו רבנן הקורא פסוק של שיר השירים ועושה אותו כמין זמר והקורא פסוק בבית משתאות בלא זמנו מביא רעה לעולם מפני שהתורה חוגרת שק ועומדת לפני הקב"ה ואומרת לפניו רבונו של עולם עשאוני בניך ככנור שמנגנין בו לצים
The Rabbis taught [in a Braisa]: One who reads a verse of Song of Songs and makes it like a song, and one who reads a verse in a place of partying out of its time brings evil to the world, for the Torah dons sackcloth, stands before Hashem, and says before Him, "Master of the World! Your children have made me like a harp with which the mockers make music."
Rashi interprets the first issue as follows:
שקורא בנגינה אחרת שאינו נקוד בה ועושה אותה כמין שיר אע"פ שמשיר השירים הוא ועיקרו שיר אסור לעשותו כמין שיר אלא בקריאתו
That one reads it with a different tune, [one] with which it is not punctuated, and makes it like a tune. Even though it comes from Song of Songs, and its root is a song, it is forbidden to make it like a song except when reading it [properly].
He further interprets the second issue as follows:
במיסב על יינו עושה שחיקותיו בדברי תורה וקורא פסוקים בקול רם לשחק בהם בני המשתה אבל אם אומרו בזמנו על המשתה כגון שהוא יום טוב ונוטל כוס בידו ואומר עליו דברי הגדה ופסוקים מענינו של יום מביא טובה לעולם
When he is sitting by his wine, he makes his jokes with words of Torah, and he recites verses loudly to cause those seated at the party to laugh. But if he recites it in its time at the party, such as on a holiday he takes the cup in his hand and says upon it words of Midrash and verses related to the holiday, he brings good to the world.
Rashi takes a very broad understanding of the problems at hand, interpreting it to mean that one is using the volume improperly, for personal enjoyment (and implicit in Rashi's second comment, where he refers to "words of Torah" and "verses related to the holiday," is that he understands the Gemara as not being limited to Song of Songs, but rather any volume of the Bible). If one sings or quotes Torah improperly, the Gemara decries him in strong terms.
The Braisa cited by the Gemara was later incorporated as Tractate Kallah 1:3, though that version poses the second problem as reciting a verse "not in its time" with no mention of a party. The pseudo-Gemara ad. loc. poses a very different interpretation of this Braisa:
היכי דמי כמין זמר כגון דזמיר ביה ודעתיה על הרהור ופסוק בלא זמנו דאמר כקינות
What is an example of "like a song"? Such as if he sang it and his intent was regarding [intimate] thoughts. And "a verse not in its time" [means] that he said it like Lamentations.
The first problem is fairly obvious; if only he would be profaning these words, that he proceeds to violate the Biblical prohibition against straying after one's eyes and heart! My understanding of the second problem is that the Torah is meant to be a privilege, not a burden, and one who recites them like Lamentations shows that he wishes he did not have the gift of Torah.
Unlike Rashi's approach, that one is merely misusing the words of Torah, Kallah Rabbasi understands that he is actively using them to sin. (Presumably the accepted halacha follows Kallah Rabbasi, rather than Rashi, as much of Jewish music and all of Purim Torah should be outright forbidden according to Rashi's understanding but would be permissible according to Kallah Rabbasi.)
Why do Rashi and Kallah Rabbasi disagree in their approaches? Why was Rashi dissatisfied with Kallah Rabbasi's answer of using Torah as romantic literature or laments that he posed his own answer instead?