I think this is a very Western-POV argument to make. Like the minimum wage argument, it stems from a belief in a fixed pool of resources being abused by robber barons, or a diluted version of the argument, which may be true in some cases. If you dislike Austrian flavored economics, it's probably not a good idea to keep reading. I will leave aside the fact that Singapore was recently targeting to be 50% immigrant in the near future (and, in practice, is still heading there), and focus on the implied criticism of Singaporean labour policy in your comment and others on this thread.
From an Asian or third world POV, Singapore is creating thousands if not millions of jobs that wouldn't otherwise exist. These workers aren't abducted from their countries and shipped in chains to be sold as free labour as used to be the case in another country just a couple centuries ago. They voluntarily seek income and non-monetary benefits such as living in a country with clean roads, a fair justice system, clean water from the tap, ample food, and pay several times what they'd get at home which goes a LOT further when sent back home to the family (source: I lived and worked in India for an Indian company, on a project involving Pralahad's "bottom of the pyramid"; never was I so grateful to be born in the West).
An illustrative example is the market for maids. Although I don't personally have a house maid, plenty of middle class income families here have a full time one because they can afford it (around $500/month + lodging and food I believe is the going rate, although the families I know pay upwards of $2000). Bump the cost of a maid to a Western minimum wage on a PPP adjusted basis, and the locals will start doing their own cooking and cleaning, and the Pinay ladies who get to spend a few years in Singapore won't have that opportunity anymore. Their jobs mostly won't go to Singaporeans, they'll just disappear, just as your illegal Latina maids in the US would disappear if "la Migra" was more thorough.
Singapore is not responsible for the policy failures of other states (indeed a strong argument can be made for Lee Kuan Yew being instrumental to the bettering of policy and prosperity in a lot of much larger states such as his influence on Deng Xiao Ping, and his part in the creation and direction of ASEAN).
As such my personal opinion, however politically incorrect in the Western ivory tower it may be, is starting to lean towards Western policies being the "inhuman" ones - "close the borders and go protectionist on your labour markets" - with a huge opportunity cost in millions of jobs that simply disappear or become illegal (as with the extraordinary 11 million illegal immigrants estimated to live in the US, over 3% of the population!) which aside from sucking more from a worker point of view, is a breach of the rule of law and therefore yet another attack on the primacy of individual rights.
A strong case can be made for the opposite argument: look at Australia for a tightly regulated foreign labour market, with high worker benefits, a comfortable welfare state, and thus a much flatter society which can be argued to be nicer to live in for citizen. It also has millions of people knocking at the door and being turned away (see any discussion about "Big Australia").
And therein lies the uncomfortable part of any immigration discussion: how do you define who gets rights? What is a citizen? Who is part of my "group"? What defines my home and what do I want in it? We Westerners benefit from excellent borders, so we do not need to think too hard about these things.