I found out recently that someone I know, (but don't know well) flushes their dog poo. Please tell me this isn't actually a thing that's okay because it seemed pretty gross to me. I don't have dogs or cats so I haven't given it any thought before. I do know that cat poo in particular can have some parasite that is pretty dangerous for people. But maybe it's okay and water treatment is good enough to clear out all the nasties.
YABU: flushing is fine and better than all the plastic poo bags going into landfill.
YANBU: It's gross and carries germs that are not adequately removed from the water during sewerage treatment.