The crux of the matter here is why people react so negatively to being recorded on video. You seem to believe it is because the person doing the recording might attack or ask for money. I don't really buy this argument, since being asked for money is not really threatening, and there are so few people who turn violent randomly that it is not something one would assume immediately of strangers.
Most likely, the reason people become angry when recorded is due to a privacy concern since they do not know what the recorder will do with the video. In this case, I think this guy does make a valid point. There is no way to tell what will happen to surveillance camera footage. Yes, theoretically it should only be used in special circumstances, but until it is codified into law, and even if it is, there's really no guarantee.
It can be, if it's someone who won't take no for an answer. I've been approached in public by mentally unstable or drugged men sometimes (certain neighborhoods here). They can be persistent. If they choose your table to sit at, they won't want to leave. In a country that took better care of its poor, they might get treatment, but that's another issue. It's unpleasant in any case.
Of topic, I know, but I find it ironic (in a bad way) that the US put many of these people on the street to save them from the even worse conditions that existed in state hospitals. As somebody with a loved-one with a serious mental illness, I don't find where we've landed to be an improvement.