This is actually a fascinating subject, and it's interesting that you make no distinction between 'swear words' (profanities and obscenities) and racially offensive language. Sexist insults seem to fall somewhere in between, as they are often both vulgar and politically incorrect. All the examples you give of so-called 'swear words' in Chinese seems to be racial insults of some kind. I wonder if this is a cultural difference between east and west? To the western mentality they are different concepts, and seen as 'inappropriate' for different reasons. Do you have Chinese 'swear words' which are equivalent to western profanities and obscenities?

It is a very common phenomenon as a means of expressing frustration. You will find that it is used often in everyday life although it is frowned upon when used unnecessarily. In films it is used for a perverse sense of humour.

It depends on the person. Some people curse in their everyday conversations and other people don't. Among younger people maybe a little more than normal, but I don't think they will talk to a person they don't know with swear words.They only talk like that when they are with their friends.