I think that in any country, it should be taboo to date ANY students at the place you work at. Obviously high schools would definately be a no-no, but I understand there are many young English teachers probably not much older than their students at university level. But because of resentment and other reasons BenDan mentions, it should be off-limits. I had a similar conversation in class last week with students when I presented the dilemma of broken relationships between boss/ worker in the same company. They couldn't believe that in the West now often companies which to be notified if there are any relationships within the company.
And yes, relationships or even sexual harrassment are so common in schools here, it's crazy! One of my old students, now in grade 3 at uni, has been chased and harrassed by her old high school teacher (married) whenever she goes home, to the point that she refuses to on the holidays. She has no idea what to do, it's a small town in Xinjiang! She contacted me for advice about it a few months ago, but I had no idea given the cultural differences here.