What is colloquially refered to as “unskilled labor” are jobs that can effectively be learned by anyone with a highschool education in a relatively short time. It has nothing to do with the skill level needed to excel at that vocation. If you take say a NASA rocket scientist and throw them into a longshoreman gig they are not going to be pulling their weight from the get go. However, they will quickly become proficient at this unskilled labor and reach an acceptable level of performance in relatively short order. If we reverse the scenario and place the stevedore into the NASA Rocket Scientist position, it will take them a much longer time to become proficient and an adequate contributor in this new role. They will need to learn a lot of math and science (arguably several years worth) that is beyond the scope of a highschool education. I am not saying they couldn't, but it would take a while.
The argument that both the stevedore and NASA rocket scientist deserve fair compensation is different from the argument than that there is no such thing as “unskilled labor”. Don't dilute your arguments with misinterpreted colloquialisms.