I get that until recently it was considered normal and relatively cheap, but you are literally paying someone else to make food for you.
It can’t be sustainable without exploitation of workers and/or animal welfare to have that available to the majority of people on a regular basis.
If you can only afford fast food as a luxury, to me that seems like a good thing.
Obv anecdotal, but in my experience people just swap to less well known, less regulated (through obscurity) brands. Or they start to roll their own using lower quality materials.