Tourism from the mainland has become such a sensitive issue in Hong Kong that the merest hint of government intervention to curb growing numbers of visitors affects the share price of companies that benefit. Chief Executive Leung Chun-ying acknowledged last week that authorities were looking into the need for a strategy, although he played down suggestions that cutting the influx by 20 per cent was on the cards. That was enough to jolt property and retail stocks, alarming shareholders and those employed in the sectors. Bosses, workers and investors don't need such uncertainties; an approach centred on our free market spirit has to be clearly articulated. Growing anti-mainland sentiment makes a response a necessity. The bigotry and selfishness shown by some Hongkongers during protests are not reason to cap numbers. Valid arguments have been put forward, though, so there may be a need for local and mainland authorities to modify policies. At the least, better research and cooperation and coordination are necessities. Numbers have risen dramatically in recent years, largely the result of the introduction in 2009 of one-year visas that allow multiple entries. Mainland visitor numbers rose to 40.7 million last year, up 16.7 per cent on 2012, almost three-quarters of the total arrivals of 54.3 million. Estimates that tourist numbers will climb to 100 million by 2020 have worried residents already fretting about the fabric of districts being altered as traditional retail outlets are replaced by those catering solely for tourists, and as streets and public transport become more crowded and rents in affected districts rise. Tourism has to be sustainable - the outcome for visitors, residents and companies has to be positive. To ensure that benefits are not detrimentally eroded, all aspects of the tourism industry have to be thoroughly debated, researched and monitored. There may well be a need to adjust policies to limit numbers. But we should also have faith in the free market to determine the flows of people, goods and services.