remember you are not in the real world. when you intervene there are many possible problems you may have to face. example if you intervene when you see someone getting pick pocketed what if a fight breaks out, you are the big bad violent foreigner attacking a chinese person. if you are very close to the situation and if you are black, and the victim is an ignorant nationalist they're more likely to believe you were stealing from them. also  it is a perceived loss of face for china if a foreigner intervenes and therefore some may be seriously upset at you. logic does not apply here. 

It is ok to intervene if you want your face kicked in by a mob..

I would say that there is no general; rule to cover all situations you describe.  It would depend basically on what is really happening, on how well you perceive what is really happening, your upbringing and principles, the mob gathered around the excitement, etc.

Why do you think that no one has intervened prior to you stepping in ?.  Because that is the most common occurrence here, do not get mixed up !.  

But if you feel like damn the consequences, then intervene, but do not cry afterwards.  I have seen cases where the mob beat the shit out of a pick pocket, and have seen many cases of a woman yelling because her purse was stolen, and no one moves a finger to stop the running guy.

I myself must either force myself not to intervene or continue walking and ignore one guy beating the hell out of a woman on the street.  But previous experience has shown me that if I do, about 90 % of the time the woman will stop yelling, and gang up with the fellow against me.  So, again, why get involved if your efforts will not be appreciated, and will get you in trouble with the local Police ?.

For you (or me), kids pissing in public is offensive, but in China is common occurrence.  What do you think it will happen if you tell parents to stop their kids from doing it ?.  Probably not much more than them thinking what a crazy laowai we have here.

In a way it is very hard to do, and even harder to accept, but you can not judge others here by your rules, but must learn and tolerate theirs.

here is why no one ever help any one in china

Yes i once help save someone from a pick pocket we then became fast friends. Then the day came when he was taken by the local mob boss because he owed him money. I rescued him but put the boss’s second in command got hurt and he came after us. We know the Chief of Police was dirty so we called one of my contacts from Interpol. We were staying in a safe house while we waited, for Interpol to find him and take him in for trial. But then they kidnap my ex-girlfriend then we know what we had to do, we had to save her and take him down once and for all. With my friends Tec skills and my training he didn’t stand a chance, or so we thought. Turns out my ex was really the boss’s daughter. she didn’t want to lie to me but her father made her. He shot my friend but then the explosives my friend had set up went off and sent his men running, He was alone. I fought him to the death but I spared him because at the last minute my ex yelled out and I know I was not that man anymore. So I knocked him out cold and called Interpol to pick him up. I picked up my friend and gave my ex one last look good bye and left into the sunset. 
 
So you know what never help anyone in china. that is like the third time that type of crap happened to me, just drink your damn tea and let him get screwed.

I would advised to stay away. China is already so complexed as it is, stay off the police radar here.

Only if the foreigner is Jiliu....

Think of it in this context: People complain and fight and steal from one another, but as soon as an outside force introduces itself to try and correct what it percieves as being an injustice (judged by an entirely different set of cultural ethics), those same people who are complaining and fighting and stealing from one another will band together in a heartbeat and turn all of that angst upon the outside force. That outsider is you. Just one look, and they can tell that you "ain't from around these parts."

And believe me, there are a heck of a lot more of them than there is of you. Be safe. Be wise. Don't get involved.

I wish I knew the answer.

I have become apathetic with time, I never intervene because it means troubles, in fact I never talk with locals except if they are hot girls or if I have business to do with them.