The "value added" by any employee is variable. In the company where I work, we have manufacturing employees that get hired, basically if they are breathing. No learned skills, other than basic existence skills. Generally no education beyond a HS diploma or equivalent.
They start at around $12 an hour, and are taught, on the job, "push this button, remove this part", etc....
They are quickly and easily replaceable. (not trying to sound cruel, just the facts of business). There is a "ladder" they can climb, if they show the ability.
Then you have the technical level, starting with equipment technicians. These people have at least a 2 year degree in some technical field. I think most of them start at around $18-19 per hour. Some of these techs have several years of experience "fixing things", and the expertise to do that.
These employees are not as easy to replace.. the requirements are more stringent.
Then you have upper level technical people... the senior technicians. Their pay is usually $20-21 and up, depending on experience/ability/tenure. Some of them have 25+ years experience.
These people are even more difficult to replace.
Then you go into the engineer level... wages go higher, depending on experience and education level. An engineer with a BS degree won't make as much as an engineer with two PhD's.....
You see the progression? Which employee adds more to the company? Which is easier to replace? Those issues, and many others contribute to the idea of "who is worth more?"
Do you think that all of those people should make the same "living wage" ? What about the manufacturing operator, with 6 kids, should he make more than the engineer tech, whose kids are all grown and gone? He probably has a higher "wage need" than the engineer, doesn't he?
Does his higher "wage need" negate the fact that the engineer spent years getting a degree, improving himself, and then more years gaining experience and knowledge? Is the "living wage" based strictly on how many mouths to feed an employee has?