Obviously, this is a provocative notion, one that I'm not even sure I agree with (I suppose it depends upon the market in question). But I like its overarching idea — that we make work pay. Lots of important, front-line jobs performed in the service of high-profit companies are seen as menial, minimum-wage work. No matter that they can be grueling and risky, often far more so than more prestigious jobs, and that society couldn't function without them — they're looked down upon by the public at large, almost as a penalty for lacking the connections/education/drive/whatever to get a better job, so those in them deserve whatever they get.
In fact, that's often how we view work in general, and it's destructive. When the workplace is seen more as a competition/value judgment than as a way to make a living, it's all too easy to forget that these people often struggle and that we foot the bill one way or another for their trouble.
That's what comes to mind for me when I hear people complaining that raising the minimum wage, or wages in general, would mean they would now be making minimum wage. I doubt that; in a market where even the lowest-wage work is competitive, higher-level jobs would have to offer more to keep up. But even if that didn't happen, so what? Why would a decent salary be so bad if it now be considered minimum wage? That would speak well of our standard of living.
When people are competitively compensated for their jobs, they will perform better, out of senses of loyalty and stability. That helps the individual and the company alike, as turnover is less likely. It gives the employee more money to spend, thus spurring the economy and in turn the company, which leads to more jobs all around. That was true for America's most prosperous decades and it's true today.
So while $40K might be steep for a cashier in most places, it would be cheap not consider some kind of bump.