If the minimum wage is set too high, it will create unemployment to people who are worth less than the minimum wage. No employer (unless he is your father) will pay a worker more than what he thinks the worker is worth. Anything more will be charity. It is not fair to expect charity from bosses because they set up companies to make money, not give away money. In a capitalistic economy, a minimum wage which is set too high will lead to higher unemployment among the young, the old and the unskilled. The young will be hit because they still have not accumulated enough work experience to be worth more than the minimum wage. The old will be hit because their market value has depreciated below the minimum wage over the years. The unskilled obviously do not have the skills to be worth the minimum wage. They will be condemned to permanent unemployment because they will not be employed in the first place. Not being employed denies them the opportunities to acquire useful skills on the job which can lead to higher salaries. At least exploitation gives the low-wage worker hopes of gaining useful skills which allows him to command a higher salary later. By protecting workers against exploitation with minimum wage, more potential damage is done. It is exploitation that allows low-paid workers to have on-the-job training opportunities that hopefully will raise their worth later on. They can job-hop to higher-paying jobs after getting enough experience, thanks to exploitation. I think if people recall their job history, some probably felt exploited during their younger days with low salary. But it was this exploitation that allowed them to job-hop to higher-paying jobs later on. Surely, temporary exploitation is better than permanent unemployment.
The most seriously hit will be the poor because they are the group with the most number of people whose market value falls below minimum wage. Instead of helping the poor, the minimum wage may end up raising unemployment among the poor. Given that social welfare in Singapore is near non-existent (due to low taxes), the consequences will be terrible for these people.
If the minimum wage is set too low, one might as well not have this rule in the first place. Why scare off investors and businessmen unnecessarily and create new administrative inconvenience?
Even if the minimum wage is set optimally initially, it will not stay optimal for long. The optimum level will be fluctuating with economic conditions. It is impossible for government officers to adjust the minimum wage optimally with changing economic conditions. If they can be so in tune with the economy, they might as well speculate in the financial markets and make a bundle.