It's extremely common for there to be human shit in the train cars, and lunatics going nuts. It's absolutely nothing like Japan.
Where does that come from? Not from your experience. You've never been on NY subways, clearly.
I've never seen feces - and anyway, how could you tell if it's from a dog? Did you examine it? Take it home and test it? It's one of the stories that maybe is slightly plausible, and which yields such strong disgust that rationality is overwhelmed and it makes a sensation - perfectly constructed misinformation or urban myth. Like waking up in a bathtub with a kidney missing.
'Lunatics' is such a loaded (and hateful) word you'll have to specify what you mean, but the occasional person talking to themself is harmless and completely uninterested in you (thus the conversation with themself) - I have never had any problem with such people on public transit or elsewhere. They are the most vulnerable people and compassion is the appropriate response.
As I wrote above, the stories are nonsense and it's induced fear.
And this is all to say nothing about the decrepit state of the stations and cars themselves.
I've also been to Japan and experienced their trains. It's in such a different league that it's almost comedy.
NGL this isn't surprising on Japanese trains either. Especially around last train. It's not super common but you see it from time to time and you just use a different car and report it to the staff next time you see someone.
So not "extremely common" as the commenter upthread said.
> liquid left on seats
As in, something spilled?
> litter
Lol. Only on a weekly or monthly basis?
> gag-inducing smelly people
I think some people are looking to be judgmental.
> antisocial behavior
That's taking it pretty far; it's easy to ignore these things which are almost always harmless - none have ever affected my life. Maybe being judgmental and (for some) hateful is the real and dangerous antisocial behavior - the consequences have had real and awful consequences for many.
> not put up with that
That's a bit controlling, insisting the world and other people must be your way. Freedom means something very different. No wonder you don't like NY.