The problem with this argument against, is that it reinforces the point it is arguing against: If a contributor cannot afford the $20/year to publish for a single 12-month period, then they are already a risk - someone could buy their account off them.

A small bar of $20/year is also enough to completely cut-down on contributors who sign up with the intention of publishing malicious packages: they have to pay $20/year for each malicious package they want to publish!