A few years ago, the elite Chinese International School of Hong Kong decided it would be a good idea to send its tenth graders to the mainland for a semester or two to perfect their mandarin language skills.

The most vociferous objections came not from long-standing Hongkongers but from locally-resident mainland parents, who insisted that they had not moved to Hong Kong just to see their kids forced to spend time back in the mainland -- even for a limited period.

Hong Kong people have made it abundantly clear in myriad ways that they have no wish for closer relations with the People's Republic of China. On two consecutive Sundays in June, millions of them turned out wearing first white then black, to protest the planned implementation of an extradition bill which would undermine the 'two systems promised with the one country' reunion of the city with "the motherland" in 1997 when the British colonial regime came to an end.

But they were not alone. As they marched, shouting slogans in Cantonese, they were joined in great numbers by Hong-Kong-resident mainlanders of all backgrounds, echoing their cries in Mandarin.

So, it would be a mistake to think that the marches are simply about pitting Hong Kong natives against edicts from Beijing. In fact, some of the most passionate opposition to the proposed legislation came from mainlanders who know best the shortcomings of their own legal system.

Prosperous mainland businessmen and investors, (who now share with local billionaires the most exclusive addresses in Hong Kong, whether on the Peak or in Deep Water Bay), have tried to persuade Carrie Lam, who was hand-picked by Beijing as Hong Kong's fourth chief executive two years ago, to abandon the proposed extradition treaty permanently rather than withdraw it for an indefinite period of time as she promised.

Over dinner with a small group of mainlanders now resident in the city on May 9, Lam, a lifelong bureaucrat, tried to address their concerns. She noted that the Philippines had a flawed legal system (implicitly admitting that the Chinese system wasn't perfect), but Hong Kong nevertheless maintained an extradition treaty with that Southeast Asian nation. She did not succeed in assuaging the apprehensions of these mainland business people.

Hong Kong Chief Executive Carrie Lam, right, and Secretary for Security John Lee Ka-chiu speak to media over an extradition bill in Hong Kong on July 2. © Reuters

Mainlanders residing in Hong Kong have good reason to fear Beijing's reach across the border. It is precisely because property rights were seen to be more secure in Hong Kong that they came to the city in the first place.

The fact that financial assets in Hong Kong can be seized under the proposed law is part of the angst on the part of mainland tycoons.

All too often mainlanders living in Hong Kong have been caught up in investigations on the mainland and faced allegations of financial crimes. In a well-known example, five years ago, Kaisa, a Shenzhen-based property development company became involved in one of Beijing's anti-corruption campaign which targeted local government officials in Shenzhen for alleged financial wrongdoing.

Kaisa's chairman, Kwok Ying Shing, was caught up in the investigation because he had ties with some of those officials. Investors, lawyers and one company official say that the company first became aware of the problems when it was not given approval to sell any of its developments.

Kwok was summoned across the border, but pleading ill health, he declined return to the mainland. There was no extradition law that could be invoked to try to force Kwok to go. He resigned as Kaisa's chairman. Unable to service its debt, since it could not generate cash from development sales, Kaisa defaulted on some U.S. dollar bonds, which traded down to as low as 30 cents on the dollar.

Eventually Kaisa and Kwok were cleared of any wrongdoing by Beijing and Kwok returned to the company. Kaisa's finances recovered as Shenzhen property boomed has and the bondholders profited, especially those who bought at the bottom.

The details of the case and its resolution were never fully disclosed -- leaving doubts why the probe was pursued in the first place. The point underlines the argument that rule of law matters.

Doubtless some in the mainland community generally have personal motives. Some face legitimate investigations for financial wrongdoing. Others may feel that cases pursued against them are totally illegitimate. Undoubtedly, some are fugitives from mainland justice. Even without the extradition law, police on both sides of the border have cooperated in returning such fugitives in a few hundred cases under circumstances which have generally been kept quiet.

But that doesn't mean the mainlanders do not also have genuine concerns over basic human rights.

Policemen stand in front of graffiti on the walls of the Legislative Council, a day after protesters broke into the building in Hong Kong on July 2. © Reuters

They have good reason to remain wary of the long arm of Beijing. What would have happened, for example, if the bill had been in place in 1989 when many mainland students fled to Hong Kong following the crackdown on Tiananmen Square protesters?

In the 22 years since Hong Kong was given back to China, anti-mainland sentiment has grown compared to the rapture surrounding the 1997 handover. Over a million mainlanders have become permanent residents of the city of 7 million. Mainlanders have been blamed for everything from shortages of baby formula to the lack of hospital beds for pregnant Hong Kong women to litter in the MTR metro as they discard their instant noodle containers, ignoring signs forbidding consumption in the system.

Because housing stock in the crowded city has not remotely kept pace with the influx and natural population growth, mainlanders are also held responsible for housing prices which are the most expensive on the planet. The finger of blame should rather be pointed at the vested interests of big property developers and the government, which cooperate to restrict the supply of building land. But that is another story.

Still, these divisive issues were mostly absent in these past few weeks. Anti-mainland sentiment has morphed into something more complicated.

Many Chinese have chosen to make their home in Hong Kong precisely because they no longer feel comfortable in Xi Jinping's China. Some of them studied abroad, making them suspect in the eyes of the regime, even though even President Xi Jinping's daughter was educated at Harvard (under a pseudonym).

As more and more mainlanders take part in these demonstrations, their presence is a timely reminder that they are as much victims of an increasingly arbitrary regime in Beijing as Hong Kongers -- if not more.