I expect everyone to be paid a living wage at every full-time job. That's the very definition.
Additionally the Fair Labor Standards Act (for US anyway) does not give any formal definition of "full time" work, and is up to the employer. Only that covered nonexempt workers working more than 40 hours are entitled to overtime.
It's fine to disagree, but at least provide some sort of substance to your argument...
It takes your full job time, it says that there is a measurable amount of job you can have and that it is full with that one. Following that logic, if you fill all of your available job time, there is an assumption (mine and others) that it would provide simply because if you can't, you need more job to do so, making it not a full-time job.
Any conclusion you come up with is completely subjective, and might fit for some people, and might not for others. Maybe someone's full-time job is someone else's part-time job.
Draw the line wherever you think it should be drawn. Their argument is still true. The argument doesn't change whether full-time is 25 hours or 75 hours.
Every single adult working whatever society agrees is "full time" should be able to live comfortably on those wages.
What sort of employee rights is the US lacking?
Why do you think people have this ability and choose not to use it? Do you think they're all too stupid to think of it?
Why would he need a source to back an opinion?