Not to leave this in tags, but @idlenight pointed out what I thought was obvious, but I'll take it even one step further than simply 'as above so below'/'made in our image' - they're facing the same kinds of problems as us, just... Much worse, even if for a much more resilient people. And I think, based on what we've seen in The Old Peace, these problems do exist across all of Tau.
As far as we know from the Lore, Sentients aren't supposed to be independent individuals at all. The Orokin made them as extremely adaptive hivemind terraformers, and as far as we currently know, their 'sentience' was gained after reaching Tau, but before the Old War, when they collectively decided to try to wipe out the Orokin to protect Tau from them. But their sentience did not remove their hivemind.
In The Old Peace, we learn of the Tau-native xenoflora called the Bloom, whose pollen somehow grants Sentients temporary individuality, hence the brokering of The Old Peace treaty. When it runs out, though, they return to the Hivemind, which is dead set on wiping out 'The Orokin' (which, to remind all, is pretty much everything in the Origin system, regardless of how far removed we are from the Orokin proper).
There's an important possible link between the Sentients becoming sentient before The Old War, and the Bloom being native to Tau. Perhaps on arriving/terraforming Tau, some of the Sentients accidentally became individuals, gained 'sentience' (not quite the correct term for it but we'll roll with it I guess), but then rejoined the hivemind after the Bloom pollen wore off, spreading their altered perspective to the rest of the hivemind...
But this is the core threat to Sentient society, which has driven them to such human societal problems as classism, corruption, crime, and gambling - the hivemind never went away, and a worse problem got stacked on top of it. Their individuality is objectively temporary, and most/all the original Bloom production was killed off (on Perita, but it's implied to be the whole shebang) due to, essentially, greedy Orokin betrayal in the conflict around The Old Peace.
So they've made an artificial, narcotic-if-overused Bloom substitute, right? Keeping them from succumbing to the hivemind and becoming monsters again. But Brysko mentions something that hasn't been expressed by/around Sentients before - the nightmares, and the screaming...
... Because whatever this black rain is, it's reanimating the dead warframes and sentients all over the place, including old battlefields (so it may not be isolated to Fornax, either...)
... And those dead, reanimated Sentients... Lack the Bloom. They're in the Hivemind. The Sentient Hivemind is now full of screaming, rotting, undead Sentients, trapped in an eternal war with screaming, rotting, undead Orokin child soldier meat mechs.
Wouldn't you do anything to escape having that in your head forever? To escape the seeming inevitability that you'll all become part of it sooner or later?
Suddenly, a rain-slicked city full of crime, drug, and sin, doesn't seem so far fetched out in old Tau, does it?
stormborns
s-u-f-j-a-n-s-t-e-v-e-n-s
andulkaphoto
yousharknotpass
prguitarman
gracieabrams
discoholicmusic
