SINGAPORE - He was born in Singapore, as was his father. He did Singapore proud, winning a gold medal at the Asian Games for the country.

And yet, for some netizens, the looks of this Eurasian prodigy were more eye-catching than his achievements.

They derisively dubbed swimmer Joseph Schooling an "ang moh" (a Hokkien term for "Caucasian") and a foreign talent.

Citing this example, Prime Minister Lee Hsien Loong on Friday touched on the dangerous anti-immigrant sentiment that appears to have gripped some Singaporeans.

If allowed to go unchallenged, it could end up harming Singapore's economy and reputation, he pointed out. "We see tendencies... to blame everything that happens in Singapore on foreigners and blame all foreigners for anything bad that any one non-Singaporean does," he said.

Singapore must avoid going down this road, Mr Lee added.

For one thing, it needs foreign professionals, managers and executives (PMEs), as they create good jobs for locals, said Mr Lee at the National University of Singapore Society's 60th anniversary event.

His speech centred on how Singapore's policies must involve both the head and the heart, and keep facts in mind.

"While we are good-hearted, we must not shy away from being hard-headed," he said. Stark realities like Singapore's rapidly ageing population and low fertility rate cannot be wished away.

"We need growth and prosperity... and you cannot get growth and prosperity just by good intentions," said Mr Lee. Singapore needs resources to grow the economy and give its people better lives, he said.

Keeping Singapore open to foreign workers is a key part of this economic growth, said Mr Lee, even as he acknowledged the dilemma that this threw up.

On the one hand, Singaporeans know that there are too few workers to build homes and MRT lines and work for companies here. On the other hand, foreign professionals vex Singaporeans because they compete with locals for good jobs.

"(But) if we are too tight on the foreign PMEs, I think many companies will be deterred from coming here and the jobs for Singaporean PMEs may not even exist in the first place," said Mr Lee.

He pointed to the balance that the Government was trying to strike on this tricky issue. While making sure that people were comfortable with the pace of immigration, the Government was keeping the inflows moderate, he said.

As for the comments hurled online at Schooling, Mr Lee said: "I am ashamed and dismayed when I read such virulent and nasty attitudes, and I am sure, so are many other Singaporeans." He added: "We have to stand up and have the courage to say so, and not be cowed into being silent."