Alan Dean Foster's situation was not an irrevocably signing over his rights; he signed a specific business agreement that Disney tried to renege on dubious claims that would totally change corporate law if it was made valid precedent.

Don Rosa's situation doesn't really have much to do with the original advocacy to do away with copyright altogether, so I don't understand your point here. Are you arguing that copyright is bad because it's sellable under unfair terms, and therefore no one should be able to sell their work?