Kundera's title reflects two of the most destructive weapons in the psychological arsenal of humanity. We don't mean to be overly dramatic, but consider this: inappropriate laughter and the ability to erase the past come together in these stories to wipe out the identities of many of the characters.
See? We told you it was pretty dramatic.
Revisionism enables the Communist Party to present whatever version of history they darn well please. The introduction of laughter into almost any situation takes away the dignity of the moment, reducing even our noblest actions to absurdity. Funerals? Love? Sex? Throw in some inappropriate laughter, and you've ruined everything. You remind us that on some level, we are all ridiculous.
If Kundera structures this work as a series of "variations on a theme," then the book is well named. We get the author's thematic preoccupations right up front.