Earlier quoted context omitted.
Haven't read the article... but my response to you is that not every "contractual" agreement is voluntary. Think people working minimum wage jobs to feed their children, or children working in sweatshops in asia. I get what you are saying... that it is a click bait title, but the fact remains that the late-stage capitalistic hierarchies that form are not totally unlike other labor systems (indentured servitude/slaver…
How is a minimum wage job not optional? People stay in their minimum wage jobs because it is better than their other options, not because the company forces them too. Really, the company giving the person their minimum wage job is more 'moral' than the other companies in the area, because the other companies offered an even worse job, or didn't offer one at all.
Because by optional we mean a totally free choice -- not merely the necessity to chose among N available options (lest you starve).
There are degrees in freedom (a rich person doesn't have to work at all if they don't feel like it), but when you're scouting for minimum wage jobs, you're at the lowest of those degrees.