When my father went to London in the 1960s for several months to prepare and take a qualifying law exam, he was told at least a few times by total strangers in the street to "go home". When my wife went to England and Wales as a foreign student in the 1980s, she was likewise told to "go home". In time, they did what they were told. So, at a gut level, I feel a bitter irony that Chinese are now being told to go home by fellow Chinese waving British colonial flags in what is Chinese territory - Hong Kong.
Look, I get it; there are two narratives here, one legitimate, the other not. The first one is that Hong Kong has finite space and resources, and cannot cope with such a large influx of mainland visitors. That has caused serious tensions and problems in our society and economy. So instead of opening the floodgates, the right response ought to be: you are welcome here like any other visitors but unlike before, there is now a regulated queue for you to join. I believe mainland officials and would-be visitors would understand and accept that.
There is another message sent by people such as those who rallied against mainlanders in Tsim Sha Tsui. It was printed on some of their banners, which said: "Locusts, die going home". The people who demand that the "locusts" get lost say they were driven to it by mainlanders' bad behaviour and other negative effects on the city. Their apologists say while their behaviour may not be commendable, it's justified given the adverse socio-economic effects of the mainland horde. But if you are rational and decent, you would send the first but not the second message. The self-styled anti-locust crowds look more like they are projecting their own hate and resentment, anxieties, fears and prejudices at a highly visible and easily identifiable group. Some otherwise intelligent and educated people use what is clearly a reasonable concern to justify and whitewash such repugnant chauvinism and bigotry.
I take it as a moral axiom that it is never right to target a particular group with labels that demonise or dehumanise them such as likening them to insects. You know this is happening when you won't get away with applying such labels to any other groups than the one targeted. Societies that allow that to happen rarely end well.