Then how are workers supposed to win better terms from their capitalist employers, outside of collective bargaining or state intervention? Is a football player being infantilized when he joins a union -- because he ought to be able to negotiate contracts by himself? When a union helps him extract a more equitable share of the profits, is he being infantilized, or is he being smart?

You're free to frame this argument in terms of individual rights or "economic competitiveness" or state paternalism. Unfortunately it amounts to little more than economic handwaving. At worst it's a disingenuous ploy to undermine the interests of the labour class, deluding workers into thinking you're giving them economic rights and freedoms ("you should be able to choose when you work!") when really you're just justifying your extraction of an even bigger share of their labour.

The common labourer has no economic power. The state, the firm, and (to a diminishing extent) unions do. I hate paternalistic states (and unions) as much as you do, but when you place no limit on firms' ability to extract labour from their workers, you end up in twisted situations where people are being paid sub-livable wages and expected to be on call 24 hours. Not because it's an economic "inevitability" (child labour inevitable? You seriously believe that?), but because it's the most amenable socioeconomic arrangement for the capitalist class.