And what happens when McDonald's introduces an automatic fry-cooker, or a machine that makes hamburgers? Just because we currently have a lot of low skill service jobs now doesn't mean that they won't be replaced by technology in the future. With the advances in robotics we can all see where this is going.
Let's assume we can separate all cooks into Grade-A, Grade-B, Grade-C, and Grade-D cooks. Grade D cooks haven't spent much time practicing cooking, and are just barely good enough at it to get a job at McDonald's, while higher grades have worked longer and harder to acquire skills.
A machine comes along and replaces all the Grade D cooks. They're pissed that they don't have a job, but they haven't really sunk much time into it, so they go find a different job. But now a machine comes along and replaces the Grade C cooks. A few may just be naturally talented, but by and large they've spent a lot more time (that they can't get back) training to be better cooks.
So they go to look for a new job as a pencil pusher, and sure enough, there are Grade A-D pencil-pushing jobs. Well, there were, except the grade-D pencil-pushing job has also been mechanized. Only people who start off with enough experience to get a Grade C job can get it.
So now we have someone who has trained, but their training is no longer useful. And to compound the problem, we put the onus (and the financial burden) on this person to get themselves retrained, assuming they even have the natural abilities to be a pencil-pusher.
Thankfully, technology has created a new job: computer developer. But this job only starts at Grade B, and then you can go to A and A+. To get to Grade B you need training, education, and experience, and all of that you are expected to acquire on your own time at your own expense. Also, since all those Grade-C and B pencil pushers are out hunting for work, there's increased competition, which means that employers can get you for less. So more training, but lower wages.