You had a legal, regulated job. No problem there. Now imagine if they didn't have to pay you as much as you were paid, if they didn't have to keep you safe, if

You had a legal, regulated job. No problem there. Now imagine if they didn't have to pay you as much as you were paid, if they didn't have to keep you safe, if you were responsible for injuries on the job, or if you were working in a meat-packing plant where injuries like lost fingers are relatively common. I don't think anyone is arguing that teenagers should not be allowed to work, but rather that they, like all workers, should be offered protections and reasonable wages if they do choose to work.