That's the official line, but I would argue that it is incorrect.
The early twentieth century proponents of minimum wages argued something very different, and I think that they were correct in their assessment, even though I totally disagree with their aims and objectives.
Go to economics 101 and look at supply and demand curves Supply and demand - Wikipedia
They're a useful tool for thought (in practice the only thing that you'll actually see in real life is the price and quantity where they meet in that place at that time, for that good service, and the assumptions of perfect competition and knowledge, and equilibrium are never ever met,
but the curves are still useful for thinking about what a going on).
If you raise the price of a good or service above the price that would prevail on the market, you will get:
More offered on that market
And less bought on that market
What those mean on a labour market are, fewer people employed, and more people looking for work.
That was exactly the idea of the early proponents of minimum wage laws
The Economic Theory of a Legal Minimum Wage
Sydney Webb was the leading British Fabian. The Fabians' were the main basis for the British Labour party (Marxian flavour socialism never really took hold in Britain, at least until after the war to make a world safe for Stalin).
In that linked paper, Webb is clear in his aims. A less hindered market for labour had created too many opportunities for ethnic minorities, women, people with disabilities, people with poor education...
In short, it provided too many job opportunities for the poorest and most vulnerable in society, far too many for Webb's liking.
What Webb points to, is the minimum wage law in the Australian state of Victoria, pricing (and forcing) ethnic minorities, women, young people, people with disabilities OUT of the labour market.
Webb isn't the only economist who sought this at that time, I can pull out some other examples.
Their aims are absolutely Orwellian, but I think that their conclusions about the effects of their proposals are correct, that pricing out of the poorest and most vulnerable, is what economic theory tells us will happen. These guys wanted everyone but WASP males, out of the labour market.
It is only later that sugar coated lies about minimum wages being to protect the poor, and to raise the incomes of the poor, appeared.
Here's the reductio and absurdum of those lies.
If raising a minimum wage above the minimum that prevails on an unhampered market, raises up those who were earning that minimum...
Why be so mean and only peg it at say $14/hour?
Why not be more generous and raise it to $100/hour? Or even better, $1,000 /hour? Just think what that would do for prosperity, and why be so mean to stop at 1,000 /hour? Why not $1,000,000?
Can you see the problem?
Assuming no other changes in the economy (like Weimar or Zimbabwe levels of inflating the money supply), how many people would still be in paid employment?
Everyone capable of understanding numbers would be looking for work at that rate, but hardly any one would be hiring at those rates.
The role of a minimum wage is to coerce employers into not hiring people from groups who are perceived (correctly or incorrectly - it's a perception, not an established fact) to have lower productivity.
In very crude terms, it stopped recent immigrants and blacks from under bidding white unionised labour on the job market.
Further on in Webb's paper, he's suggesting state unemployment pay.
Before minimum wages, and union coercion, there was not long term unemployment. There might be short periods of widespread unemployment, as an inflationary Bubble burst and the mal investments were liquidated, but people generally found new jobs very quickly.
The post world war 1 situation in Britain is exceptional, unionisation was encouraged in the war, and there were laws preventing the reduction of wages. There was also very generous unemployment dole. The british pound had also been drastically over printed (the war was founded largely by money printing)
The pre war pound was a measure of gold, and exchanged for $4.86 us gold dollars. Due to the amount of paper notes printed, it would have exchanged for $3.20 after the war.
The British government decided (in absolute lunacy!) To go back onto gold at the old par of $4.86. this meant that the pound was drastically over valued, making british exports vastly in competitive, compared to imports. Hence Britain had massive long term unemployment and economic depression between the wars, even when everywhere else was booming in the 1920s.
The cause was governmental and was nothing to do with any inner contradictions or tendencies of unhampered markets.
Again in the great depression and in the Hoover interventions (Carried on by FDR in the new deal - the painting of Hoover as somehow laissez-faire was FDR election propaganda, and doesn't stand scrutiny) the long term unemployment was caused by government forcibly preventing the markets to clear.
And the brunt of the unemployment was borne by the poorest and most vulnerable (check out the ethnic and religious composition of the people chosen for Eleanor Roosevelt's model communities in West Virginia, to see what the racial and religious prejudices of the administration were, and who was to be "helped" at the expense of whom).
