You just answered your own question. Just because one person will do it does not prove that there are enough people in sufficient quantities willing to perform these tasks. But I'm sure you are smart enough to realize that.
If that is the case, maybe, just maybe, we need to promote better work ethics in our children. Maybe they need to get off their fat ass and learn some algrebra (other thread), do some manual labor, work off the pounds physically instead of just eating low-calorie chips while watching the Simpsons.
Last i checked, not everyone can be the president of a large company, or the main attorney from a large firm. There just aren't enough jobs in the country for everyone to have their job of choice. Also, there is nowhere near enough jobs in the US for everyone in THE WHOLE WORLD. 6 billion people on the planet, only 300m here, and you think giving away 30m American jobs will help employ everyone around the world? Hardly. All it does is increase work force supply pressure, and decrease local wages. The cost of goods never decreases, only the quality.
My example shows how someone can, through hard work and persistence, progress from the most basic job up to the higher levels. This should be promoted instead of ridiculed as an oddity.
If the purpose of the open border fanatic is to increase the standard of living around the world... then you do that by promoting stability within the target country and purchasing goods and services from their corporations, placing tariffs appropriately. Over time, their corporations would flurish , local economies would grow, and the people would prosper. You don't have the capitalists from here, go over there, bride some officials and create factories that would be shutdown in a heartbeat in the US due to horrible working conditions. This is not helping the people here or there at all, but it does put huge amounts of money into the pockets of those greedy few (with which they buy spin doctors to counter any arguments contrary to their plans).