Now (in 2022), this film is exactly fifty years old; It is almost a museum piece, a testimony of a bygone era! Of course, the comments of the other viewers are pertinent: the songs are good, most of the actors are good (& Bernard Blier is excellent), there are hilarious moments and the general atmosphere of the film exsudes the irreverent and carefree seventies. In one scene ("Cene"?) of the movie, some may have missed that it is literally a 'cut and paste' of Leonardo Da Vinci's very famous painting "The last supper"...
But there is a serious aspect to all this. Jean Yanne (in spite of his uncouthness, which may be repulsive to some) and Gérard Sire (his dialogue-writing partner for this film, who in 'real life' was an outstanding radio host) were two authentic artists, and as such were able to capture the deep-running mood of the general French public of their days. This mood (which they contributed to uncover long before it became widespread) was "derision".
Derision is not solely cynicism. In its French variety, it is a complex turn of mind in which nothing is important, no authority is respectable, no act has consequences; and at the same time I (the derisive individual) know all the answers, can pass all judgments, and can dismiss any and all opposing views without need for refutation.
There has been in France - between the '70s and the '90s, and even up to the '00s decade - a spirit of derision which has pervaded society and contributed to a gradual decrease in the usefulness and credibility of the political debate. The media which has embodied this "spirit of derision" for thirty years and more has been the TV channel "Canal plus", launched in 1984.
"Tout le monde il est beau, tout le monde il est gentil" is thus a kind of signpost for times that have not changed for the better. ___ .