This is from MC Solaar's RMI, a song about injustices done to the underprivileged:
Le monstre aux yeux verts, synonyme de la jalousie
Taxe l'eau du Sahel juste pour remplir son jacuzzi
Mais c'est comme ça que ça fonctionne...
...dans ce monde de taches ?
Dans ce monde de taches translates directly to "In this world of spots/smudges?"
I understand it's a rhetorical question meaning something like "in this terrible world?" or something. Do smudges (taches) refer to bad people?
Tache is slang for a loser (a dud), not necessarily a bad or dishonest person but a derogatory term nonetheless. It's very modern slang, I have a 20th c. slang dictionary and it isn't in it.
I don't know for sure where it comes from. Most likely from the colloquial phrase faire tache which means "to stand out in a conspicuous or ridiculous way".
Un monde de taches → a world of losers.
Indeed, "une tache" is primarily a spot, a smudge.
By extension, it is a slang word to designate metaphorically someone who "does not fit correctly" : incompetent, inept.
It is used in France since the 90's approximatively.
